PROCEEDINGS OF THE UNITED STATES NATIONAL MUSEUM
SMITHSONIAN INSTITUTIONU. S. NATIONAL MUSEUM
Vol. 103 Washington : 1953 No. 3322THE FRESH-WATER TRICLADS (TURBELLARIA) OF ALASKA
By Roman Kenk
IntroductionIn 1948, during an investigation of biting insects in Alaska con-ducted by the Bureau of Entomology and Plant Quarantine, UnitedStates Department of Agriculture, Dr. Reese I. SaUer collected andtransmitted to me several samples of fresh-water triclads (planarians)
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An examination of the material revealed that the worms belonged tothe genus Polycelis, a genus fairly common in Asia and Europe butonly twice reported from North America. The finding suggested acloser relationship of the Alaskan fresh-water fauna with that of EastAsia. A more thorough study of the triclads of Alaska promised toyield a more definite understanding of these zoogeographical relations.My field trip ^ to Alaska was made in the sunmaer of 1950. Sincethe available time was rather limited, the collecting was done mainlyalong the highways of the territory and in the vicinities of PointBarrow and Umiat.The following roads and fresh-water localities were visited on thetrip: Steese Highway in the section between Fairbanks and BirchCreek (milepost 103); Elliot Highway, from Fairbanks to Livengood;tundra lakes and pools in the vicinity of Point Barrow; ColvUleRiver, several streams, and a lake near Umiat; Mount McKinleyPark Road, a section of about 15 miles adjoining the railroad station;Glenn Highway, from Anchorage to Glenallen; road from Palmer to
' This study was supported by the Arctic Institute of North America under contractual arrangementwith the OfBce of Naval Research.238538?53 1 163
164 PROCEEDINGS OF THE NATIONAL MUSEUM vol. losWillow; road from Anchorage to Potter; and Richardson Highway,section between Valdez and Glenallen.No fresh-water triclads were found by me either at Point Barrowor at Umiat. I received, however, from the U. S. National Museum,a sample of triclads collected by P. F. Scholander in a lake near Umiat.The relative scarcity of planarians in tundra lakes and pools may bedue to the high acidity of the waters or to the extremely severe con-ditions prevailing in them during the long winter season.Grateful acknowledgment is made of the very helpful cooperationwhich was extended to me by several agencies in Alaska: The ArcticResearch Laboratory, Point Barrow; the U. S. Public Health Service,Anchorage; the Alaska Road Commission, Fairbanks, Anchorage, andGlenallen; and the Division of Forestry, Bureau of Land Management,Fairbanks and Anchorage. I also wish to express my indebtedness toProf. Edward G. Reinhard of the Catholic University of America andto Dr. Fenner A. Chace, Jr., and Dr. Doris M. Cochran of the U. S.National Museum who kindly permitted me to use their laboratoryand office facilities in Washington, D. C.Four species of fresh-water triclads were collected in Alaska. Twoare inhabitants of the White Mountains, a mountain range extendingin an east-west direction north of Fairbanks. The other two arewidely distributed in waters of the Alaska Range and of the southernsection of Alaska and one of them reaches as far north as Umiat.Family PlanariidaeGenus Phagocata LeidyPhagocata niveau new speciesFigure 21; Plate 6, Figure 1Description.?This is a slender, rather delicate species. Maturespecimens measure up to 8 mm. in length and about L5 mm. in width.In the quietly gliding animal the anterior end is truncated,with a veryslightly bulging frontal outline and with rounded lateral corners(auricles) . There is no distinct narrowing or neck behind the auriclesand the lateral margins of the head are approximately parallel. Behindthe head, the body widens and soon reaches its greatest width. Fromthere on, the lateral margins of the body run parallel up to the levelof the mouth, to converge agam in the postpharyngeal region and tomeet in a bluntly pointed posterior end.The species lacks pigment and usually appears white and somewhattransparent. The intestinal contents may shine through the bodywall and give the animal a certain amount of color; the margins of thebody, the head region, and the areas occupied by the pharynx and thecopulatory apparatus, however, are always white.
FRESH-WATER TRICLADS OF ALASKA?^KENK 165There are two rather small eyes, situated close together (about one-fourth the body width apart at the level of the eyes) and far removedfrom the frontal end. This character, easily recognized in life, dis-tinguishes the species from another white triclad with which it sharesits habitat, Dendrocoelopsis alaskensis, described as new on p. 178.The pharynx is inserted, in sexually mature specimens, somewhatbehind the middle of the body and measures about one-sixth of thebody length. The copulatory organs occupy the anterior half of thepostpharyngeal region.The animal moves by gliding only; crawling movements, such asare seen in other triclads, particularly in those equipped with anterioradhesive organs, have not been observed in this species.From the description it may be seen that the species in life showsa close resemblance to other species of the same genus, particularlyto the American Phagocata morgani, the European P. albissima, P.vitta, and related forms. A separation of these species can be madeonly on the basis of anatomical characters.Only those characters of the digestive system that have a taxonomicsignificance are discussed here. The pharynx has a structure typicalof the family Planariidae; i. e., the fibers of the internal muscle zoneare arranged in two distinct layers, a thick inner circular layer and anarrower outer longitudinal one. The anterior intestinal trunk bears10 or 11 branches on each side. Each posterior trunk has 21 to 27lateral branches and numerous short medial branches in both thepharyngeal and postpharyngeal regions.The testes are numerous and are arranged, on each side of themidline, in a longitudinal zone extending from a short distance behindthe ovary almost to the posterior end of the body. Their position ispredominantly ventral, below the intestinal branches. Only a fewtestes extend into the mesenchymatic "septa" between the branchestoward the dorsal side.The two ovaries are typical, each situated approximately below thesecond intestinal branch. An undifferentiated mass of cells, the par-ovarium, is attached to the dorsolateral side of each ovary.The genital pore (pg), situated about halfway between the mouthand the posterior end of the body, leads into a small cavity (ac)which continues to the left and dorsally into the duct of the copulatorybursa (bd) and to the right and anteriorly into the male atrium (am)
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This cavity may be considered to represent a common genital atrium.In some specimens, however, there appears to be no differentiationof the atrium into male and common parts, and the bursa duct andan undivided atrium meet at or near the genital pore. These varia-tions are obviously due to the different states of muscular contractionin which the animals were killed. The atrium, narrow at the genitalaperture, widens as it extends forward, to the right side of the midline.
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It is lined with a tall, glandular epithelium, the cells of which projectinto the cavity in a villuslike fashion. Below the epithelium thereare two layers of muscle fibers, one circular and the other longitudinal.The penis consists of a spherical, muscular bulb embedded in themesenchyme, and a moderately large papilla projecting into the maleatrium. The bulb is pierced by numerous gland ducts which openinto the lumen of both the bulb and the papilla. The shape of thepapilla is subject to great variation, due apparently to the state ofcontraction of the organ. It may be twisted to one side and evenpartly inverted into the lumen of the penis (similar to the pseudo-flagellum of various dendrocoelids) . The shape shown in figure 21appears to be that of the organ at rest. The outer wall of the papillais covered with a tall to cubical epithelium similar to that lining theatrium. Below the epithelium there is a layer of circular musclefibers followed by another of longitudinal fibers. The shape of thepenis lumen {Ip) is as changeable as that of the papilla. Typically,it appears to be wider in the bulb than it is in the papilla, thoughthere is no distinct ejaculatory duct differentiated. The lumen opensventrally to the tip of the papUla. The two vasa deferentia {vd)penetrate the penis bulb from both sides and empty into the penislumen separately, but not far apart.The two oviducts converge at the level of the copulatory apparatus,the left one passing between the bursa duct and the male atrium, andunite at a point dorsally to the atrium. The rather long commonoviduct {ode) curves ventrally and opens into the posterior part of themale atrium. The terminal sections of the paired oviducts and thegreater part of the common oviduct receive the outlets of numerouseosinophilic glands, the cell bodies of which are scattered in the sur-rounding mesenchyme, particularly dorsally to the atrium.The copulatory bursa (6) is of moderate to large size and is ir-regularly lobed. The bursa duct or stalk {hd) is wide, runs posteriorlyto the left of the midline, and curves ventrally to reach the genitalaperture. It is lined with a tall, glandular epithelium and surroundedwith a strong muscular coat consisting of intermingled circular andlongitudinal fibers.Taxonomic position.?The genus Phagocata Leidy (FonticolaKomarek) in its present extent (cf. Hyman, 1937, pp. 300-302) hasrepresentatives in Europe, Asia, and North America. The genus isnot quite homogeneous and will probably, in due time, be subdividedinto several genera (cf. Beauchamp, 1939). For the purpose of com-parison, we may consider here only those species of the genus thatlack pigment. Though the presence, or the lack, of pigment is acharacter of subordinate taxonomic value, it may nevertheless servewell as a character of specific rank. The Alaskan form differs from
FRESH-WATER TRICLADS OF ALASKA?^KENK 167European species such as P. vitta (Duges) and P. albissima (Vejdovsk^)and from the American white P. morgani (Stevens and Boring) mainlyin the structm-e of the male copulatory organ. Asia has severalspecies of Phagocata, the majority of them pigmented forms. Of thethree unpigmented Asiatic species that may belong to the genus, two
Figure 21.
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Phagocata nivea, diagram ot the copulatory organs In longitudinal section,X 92. ac, common atrium; am, male atrium; b, copulatory bursa; bd, bursastalk; Ip, penis lumen; o, mouth; ode, common oviduct; pg, genital pore; vd, vas deferens.have been described from immature specimens and the anatomy oftheir reproductive systems is not known: Planaria pellucida Ijimaand Kaburaki (1916) from Sakhalin and a species from the Bailialregion assigned tentatively to Fonticola by Bazikalova (1947). Athird species, Phagocata coarctata (Arndt, 1922), from the vicinity ofVladivostok, is sufficiently well Imown, although no fully matureindividuals of this species have been studied. P. coarctata differsfrom P. nivea externally in being smaller and broader, and in havinga different contour of the anterior end, which bears protruding laterallobes, and a greater distance between the two eyes. Anatomically,the two species are, undoubtedly, closely related.^
' Livanov and Zabusova (1940, p. 146) state that a reexamination of Amdt's slides of PUmaria coarctatashowed that the arrangement of the muscle fibers of the pharynx conformed with the dendrocoelid type(circular and longitudinal fibers of the internal muscle zone intermingled). Amdt (1922, p. 108) describedthe anatomy of the pharynx in minute detail and indicated, both in a figure (pi. 4, fig. 7) and in the text,a typical planariid pattern. I must assume that some confusion occurred somewhere, probably in theidentification of the slides sent to Livanov.
168 PROCEEDINGS OF THE NATIONAL MUSEUM vol. io3In Phagocata nivea the penis lumen opens usually below the tip ofthe penis papilla. This character has been used by Livanov andZabusova (1940, p. 96) to segregate a group of Asiatic species fromPhagocata and to place them in a new genus, Penecurva. The samecharacter is found, however, in a common North American species,Phagocata morgani, which shows no other close relations with theAsiatic group. This character is apparently inadequate as a basisfor the establishment of a new genus.Holotype.?On one slide, USNM 22332, creek crossing EUiot High-way at milepost ^31.0, July 24, 1950.Distribution and ecology.?Phagocata nivea was collected in cool,fast mountain streams on the slopes of the White Mountains, a rangenorth of Fairbanks. The temperature of the water ranged from 3.2to 7.2? C. (July). The animals are cold-stenothermic and do nottolerate sudden increases in temperature. They were often foundin the company of another white triclad, Dendrocoelopsis alaskensis.Stream on Steese Highway (pi. 8), at milepost 84.0, altitude 2,700 feet, July19 and 21, 1950, water temperature 6.9? C; one immature and one mature speci-men, from under stones.Willow Creek, on Steese Highway, at milepost 96.6, altitude 2,100 feet, July19, 1950, 7.2? C; two immature specimens, from under stones.Spring and stream on Steese Highway, milepost 82.5, near Alaska Road Com-mission camp, July 21, 1950; two mature and six immature specimens, on theundersides of stones.Fox Gulch, on Elliot Highway, milepost 1.2, July 24, 1950, 6.0? C, one smallspecimen near bait (beef liver).Creek crossing Elliot Highway at milepost 31.0, July 24, 1950; 39 specimens,about half of them mature, collected under stones (holotype).Genus Polycelis EhrenbergPolycelis borealis^ new speciesFigure 22; Plate 6, Figure 2Description.?Mature animals are usually 12 to 15 mm. long and1.5 to 2 mm. wide (larger specimens, measuring up to 20 mm. inlength, have been seen). The frontal margin is slightly convex. Atthe lateral corners of the head there is a pair of elongated, bluntlypointed auricles which are held raised when the animal is glidingquietly. Behind the auricles, the body first narrows slightly, thengradually widens, reaching its greatest width at the level of thepharynx. Behind the pharynx the body tapers to a moderatelypointed posterior end.The color of the dorsal side is usually a uniform light or darkbrown, that of the ventral side a light grayish brown. In animals
' The large highways of Alaska are marked with wooden mileposts indlcatmg only full miles. Manyposts were missing at the time when the collections were made. Fractional milages were usually estimatedfrom the nearest milepost or from the speedometer readings of the car used.
FRESH-WATER TRICLADS OF ALASKA?^KENK 169from some localities, an indistinct lighter median line occurred dor-sally in the prepharyngeal region, with lighter areas above the pharynxand the copulatory organs.The species has many small eyes (a generic character) arrangedin a band along the frontal margin of the head, the base of the auricles,and the lateral margins of the body a short distance behind the head.Anteriorly the eyes are placed in more than one row, somewhatirregularly scattered ; behind the head they are in a single row reachingbackward about one-third to one-half the length of the prepharyngealregion. There is no narrowing of the band of eyes at the base of theauricles.The pharynx is inserted at about the middle of the body andmeasures in length almost one-fourth the length of the body. Thecopulatory organs occupy more than half the post-pharyngeal region.The animal moves by gliding only.The pharynx of Polycelis borealis is structurally typical of the genusPolycelis and of the family Planariidae, the muscle zone being formedby two distinct layers, a thick circular layer adjoining the epitheliumof the pharyngeal lumen and a thinner layer of longitudinal fibers.The anterior trunk of the intestine bears 5 to 6 lateral branches.The numerous, fairly large testes are arranged in two zones, tothe right and left of the anterior intestinal trunk, extending from thelevel of the ovaries posteriorly to the base of the pharynx. Thetestes are essentially ventral, though individual vesticles may extenddorsally in the mesenchymatic spaces between the intestinal branchesand occupy almost the entire dorsoventral diameter of the body.Where intestinal branches are present, however, the testes developonly below them. Each zone of testes reaches laterally only littlebeyond the ventral nerve cord.The ovaries are situated behind the first pair of lateral branches ofthe anterior trunk of the intestine.The genital pore (j)g), situated in the midline behind the middle ofthe postpharyngeal region, connects with a narrow posterior extensionof the genital atrium (a) . This extension leads dorsally and somewhatto the left into the duct of the copulatory bursa and anteriorly intothe widened portion of the atrium containing the penis. There is nomarked division of the atrium into a posterior common atrium andan anterior male atrium. The wall of the atrium is lined with acubical epithelium and equipped with two muscle layers, one circularand the other longitudinal.The penis consists of a bulb embedded in the mesenchyme and apapUla projecting into the atrium. Neither of the two parts is verymuscular. The shape of the penis, particularly of the papilla, is very
170 PROCEEDINGS OF THE NATIONAL MUSEUM vol. i03
changeable. In specimens that were fixed in a well-extended condi-tion, the bulb appears spherical and the papilla has a conical shape.The bulb contains a spacious, irregularly lobed cavity, the seminalvesicle (vs). Numerous gland ducts empty into the lumen of thebulb after entering the bulb, particularly from its anterior surface,and penetrating between its muscle fibers. The ducts are filledwith a granular, slightly eosinophilic secretion. The two vasadeferentia (vd) open into the seminal vesicle separately from theanterolateral sides.The penis papUla is conical or finger-shaped when well extended. Itis covered with a cubical epithelium below which there are two ratherfeebly developed muscle layers, tapering in thickness toward the tipof the papilla: a layer of circular fibers adjoining the epithelium anda thinner layer of longitudinal ifibers. The absence of a strong mus-cular wall probably accounts for the great variation in the shape ofthe penis papilla observed in the material. The lumen of the seminalvesicle continues into the papilla as a wide canal (de), opening at ornear (ventrally to) the tip of the papUla. The canal is lined with anepithelium of cubical cells and lacks the gland openings character-istic of the seminal vesicle. It corresponds to an ejaculatory ductbut it apparently has no distinct muscle coat.The two oviducts, riuming posteriorly along the ventral nervecords, bend dorsally and medially at the level of the copulatoryorgans. The left one passes through the space between the atriumand the bursa duct and unites with the oviduct of the right sidedorsally to the atrium. The common oviduct {ode) runs ventrallyand opens into the posterior part of the atrial cavity. The terminalsections of the paired oviducts and a section of the common oviductare equipped with strongly eosinophilic shell glands.The copulatory bursa (6) is a large sac with a lobed outline. Itconnects posteriorly with a duct of almost uniformly wide diameter,the bursa stalk (bd). The duct runs first posteriorly, to the left ofthe penis bulb, then curves ventrally and opens, from the dorsal side,into the narrow terminal portion of the atrium, close to the genitalpore. The bursa stalk has a strong coat of intermingled circular andlongitudinal muscle fibers. There is no histological differentiationinto anterior and posterior sections of the bursa stalk.Taxonomic position.?Polycelis borealis is the second species of thegenus Polycelis to be found on the North American continent. Theother species, P. coronata (Girard), reported from Wyoming and SouthDakota (Hyman, 1931), resembles it closely in external appearanceand probably cannot be distinguished from it in life. In both species,the shape of the anterior end is very similar. The auricles of P.borealis are perhaps a trifle longer and more pointed than those of P.
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 103, PLATE 6
Sketches of living specimens of the four Alaskan triclad species, all XIO: 1. Phagocatanivea; 2. Polycelis borealis; 3. Dendrocoelopsis piriformis, striped form; 4. Dendrocoelop-sis alaskensis.

FRESH-WATER TRICLADS OF ALASKA?KENK 171
coronata. Hyman (1931, p. 126) states that in P. coronata thecurved band of eyes narrows as it crosses the base of the auricles;no such narrowing has been seen in P. borealis. These differencesare, however, insignificant and do not permit a clear separation ofthe two forms. The same may be said of other species of the genus,which likewise could be confused with the American forms in life:the Japanese species, P. auriculata and P. karafto; and P. schmidtioccurring both in Kamchatka and in Japan. These forms differfrom each other more clearly in their anatomical characters.bd ode
Figure 22.
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Polycelis borealis, diagram of the copulatory organs in longitudinal section,X 70. a, atrium; b, bursa; bd, bursa stalk; de, ejaculatory duct; o, mouth; ode, commonoviduct; pg, genital pore; vd, vas deferens; vs, seminal vesicle.To gain a better insight into the systematic relations of Poly-celis borealis to other species of the same genus, it is necessary to reviewthe present state of the systematics of the genus. The genus Poly-celis has a muscular pattern of the pharynx typical of the familyPlanariidae; the oviducts unite, without embracing the bursa stalk,to form an unpaired terminal oviduct; the testes are situated in theanterior part of the body only; the male atrium is not surroundedby radial muscle plates; and the eyes are numerous. The genusthus defined (Kenk, 1930) has today about twenty species. It maybe subdivided into subgenera on the basis of structural charactersof the copulatory apparatus.Subgenus Polycelis, lacking adenodactyls and lacking an excessivedevelopment of the muscle coat of the male atrium. This subgenusincludes Sorocelides Sabussowa (1929, p. 521) and Polycelidia Zabu-sova (1936, p. 152), both described as distinct genera. The subgenuscomprises the following species:
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Polycelis nigra (O.F.MulleT), Europe P. polyopis Zabusova (1936), Kam-P. receptaculosa (Livanov and Zabusova, chatka1940), Teletskoe Lake in the Altai P. karafto Ijima and Kaburaki (1916),Mountains SakhalinP. eburnea (Muth, 1912), Aral Sea P. sopporo (Ijima and Kaburaki, 1916),region JapanP. ttfeeftca Hyman (1934), Tibet P. coronata (Girard, 1894), WyomingP. koslowi (Zabusov, 1911), Tibet and South DakotaP. elongata (Sabussowa, 1929), Kam-chatkaSubgenus Seidlia Zabusov (1911, suppl., p. 7), distinguished by anextraordinarily thick muscle zone surrounding the male atrium.Zabusov's (1916, p. 273) genus Rjabuschinskya likewise belongs here.Species of the subgenus:Polycelis sabussowi (Seidl, 1911), in- P. schmidti (Zabusov, 1916), includingeluding Seidl's species Sorocelis P. ijimai Kaburaki (1922), Kam-sabussowi, S. lactea, S. stummeri chatka, Kurile Islands, and Japan(cf. Kenk, 1936), Turkestan P. auncu/a<a Ijima and Kaburaki (1916),P. relicta (Sabussowa, 1929), Kamchatka JapanP. eurantron (Zabusova, 1936), Kam-chatkaThe third subgenus, Ijimia Bergendal (1890, p. 326), is charac-terized by possessing solid adenodactyls
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Polycelis felina (Dalyell), including P. linkoi Zabusov (1901), Onega LakeP. cornuta Johnson, Europe and in European RussiaNorth Africa P. oculi-marginata (Palombi, 1931), NewP. tenuis Ijima, Europe and western Guinea (see Beauchamp, 1947)AsiaTwo species of the genus Polycelis are too mcompletely known topermit their assignment to either the subgenus Polycelis or Seidlia:P. eudendrocoeloides (Sabussowa, 1929) from the Kamchatka Penin-sula and P. tibetica (Zabusov, 1911, p. 349) from Tibet (P. tibeticaHyman, 1934, will have to be renamed if it should prove to be differentfrom Zabusov's species)
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Polycelis borealis is clearly a member of the subgenus Polycelis.It differs from P. nigra in having weU-developed auricles; from P.elongata, P. polyopis, and P. sapporo, in the arrangement of the eyes;and from P. coronata and P. receptaculosa in the structure of the malecopulatory organ. The reproductive system of P. karafto has not beendescribed adequately and thus does not permit a comparison withthat of the Alaskan species. The remaining species of the subgenus,P. eburnea, P. koslowi, and P. tibetica Hyman, two of which are knownonly from the study of preserved specimens, agree with P. borealisin being pigmented forms with prominent auricles and in havinga similar anatomy of the copulatory organs. The four species are
FRESH-WATER TRICLADS OF ALASKA?KENK 173
undoubtedly very closely related; whether some of them are identicalor are the same as the Alaskan form cannot be established on the basisof present knowledge. The Alaskan Polycells, therefore, is describedas a new species,Holotype.?On three slides, USNM 22333, clear spring on the roadfrom Palmer to Willow, 20.1 mUes from Palmer, altitude 3,800 feet,Aug. 9, 1950.Distribution and ecology.?Polycelis borealis is a very common speciesoccurring in mountain streams in the southern part of Alaska (AlaskaRange, Talkeetna Mountains, Chugach Range). Typically itinhabits clear, cold, fast-running waters. It has also been found,however, in several small mountain lakes which connect with streamsin which the species lives. It has not been observed in sUt-bearingglacier streams.The typical temperature range of the habitats was between 3.0?and about 15? C. (August 1950). Temperatures above 15? C. (upto 22.4? C.) were encountered only rarely and only in habitats whichpresumably have great diurnal temperature amplitudes (shallow lakes,small exposed streams).The great majority of the specimens collected was asexual. Sexuallymature animals were seen in only 6 of the 31 localities in which thespecies was found. In some localities, a large percentage of the speci-mens exhibited freshly regenerated heads or posterior ends, indicatingthat vivid asexual reproduction was taking place.Clear springs on the road from Palmer to Willow, 20.1 miles from Palmer,altitude 3,800 feet, Aug. 9, 1950, water temperature 3.0? C, numerous specimens,five mature (holotype).Clear, fast mountain stream crossing Mount McKinley Park road, 5.5 milesfrom the railroad station; Aug. 5, 1950.Streams on road from Palmer to Willow 11.9, 18.0, 19.2, 20.2, 21.6, 22.1, 22.8,and 34.0 miles from Palmer, and Ice Lake, 20.4 miles from Palmer, Aug. 9, 1950.Streams on Glenn Highway (Anchorage to junction with Richardson Highwaynear Glenallen) at mileposts 33.1, 33.9, 43.5, 64.8, 89.4, 98.8, and 117.1; Aug. 11and 13, 1950.Streams on road from Anchorage to Potter 2.9 (Campbell Creek), 10.3, and 10.6miles from the city limits of Anchorage, Aug. 12, 1950.Streams on Richardson Highway (section between Valdez and Glenallen) atmileposts 20.5, 25.5 (22.4? C), 26.3 (see pi. 7), 29.0, 37.3, 54.7, 62.6 (see pi. 7),81.0 (Squirrel Creek), and 87.5 (Rock Creek), and lake at milepost 27.3 (22.1? C),Aug. 15, 1950.Polycelis borealis was also identified in samples of triclads collectedby Dr. Reece I. Sailer in July and September 1948. The followinglocalities were represented: Richardson Highway, mileposts 8.3, 187.5,192.9, 209.7, 223.6 and 239.9, and Glenn Highway, milepost 117.1.
174 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 103Family DendrocoelidaeGenus Dendrocoelopsis KenkDendrocoelopsis piriformis, new speciesFigure 23; Plate 6, Figure 3Description.?Sexually mature specimens of this rather broad andplump species measure up to 15 mm. in length and 3 mm. in width.In quietly gliding animals, the head is truncated, with a convexfrontal margin (grasping organ). There is a visible subterminaldepression corresponding to the adhesive surface of the graspingorgan or sucker. The rounded lateral corners of the head are formedby the auricles, which protrude only little laterally, thus causing aninsignificant narrowing (neck) to appear behind them. Behind thehead, the body margins widen gradually. The greatest width isreached at the level of the mouth. Behind that level, the body tapersagain to a bluntly pointed posterior end. When the animal is atrest, the body appears short and wide, about pear-shaped, the bodymargins often forming a wavy or irregular contour. Yoimg specimensare more slender and their lateral margins are more nearly parallelwhen they are in gliding motion. At rest, however, they assume thesame pyriform shape as the adults. In short, the habit of the speciesmay be described as resembling that of European and Asiatic repre-sentatives of the genus Bdellocephala Man, with which it has in com-mon the broad shape and the anterior grasping organ.The two eyes are situated on the dorsal side of the head. Theirdistance from each other amounts to somewhat more than one-thirdthe width of the head at the level of the eyes. The distance of eacheye from the lateral margin is smaller than the distance from thefrontal margin.The color of the dorsal side is usually a cloudy brown or darkbrownish gray. In some specimens, the pigment is arranged indefinite longitudinal stripes: one sharply marked median stripe flankedon each side by a light (usually yellow) band ; laterad to this band thebody darkens, losing its pigment again near the lateral margin. Inother specimens, lacking the two light dorsal bands, the back may beeither uniformly pigmented or may show a more or less distinct darkerband along the midline. Young specimens and striped adults clearlyshow the finer disposition of the pigment in small rounded dots, eachdot apparently corresponding to an individual pigment cell.The pigment pattern of the dorsal side of the head is quite charac-teristic. A very dark field between the eyes extends anteriorly toboth sides of the grasping organ. The area above the organ is unpig-mented and white, and so are the two elongated ocular areas antero-
FRESH-WATER TRICLADS OF ALASKA?KENT 175laterad to the eyes. A pair of indistinct, converging streaks of lightercoloration may run posteriorly from the lateral angles of the head.The ventral side is light gray.The pharynx is situated, in mature animals, behind the middle ofthe body; the mouth, at the beginning of the last third of the body;and the genital aperture, midway between the mouth and the hind end.The normal locomotion of the animal is quiet gliding. When dis-turbed, it may attach itself to the substratum (apparently with themarginal adhesive zones) or move by "crawling." Young specimensdo not crawl as readily as do adult ones.The grasping organ, or sucker, in living animals, appears as a well-marked bulge on the frontal margin of the head, showing a concaveventral depression. In preserved specimens, the frontal margin isgenerally curved ventrally and the site of the organ forms a thick,grooved rim. Anatomically, the organ consists of glandular andmuscular elements. The subterminal adhesive surface is covered withan epithelium devoid of rhabdites and pierced by numerous glandducts filled with a granular, eosinophilic secretion. The cell bodiesof the glands are scattered through the mesenchyme of the anteriorhalf of the prepharyngeal region, particularly above the intestine.The gland ducts run anteriorly in dense bundles and, in their terminalsections, are thickly swollen with secretion. The muscular system ofthe organ, which could not be analyzed in detail on account of thedensity of the glandular structures, has fibers attached to the adhesivesurface, serving presumably as retractors.The rather short and thick pharynx is structurally typical of thefamily Dendrocoelidae; its internal muscular zone consists of inter-mingled circular and longitudinal fibers.Auricular sense organs are represented by two bands of sensoryepithelium extending posteriorly from the sides of the frontal margin.The cells of this epithelium are less tall than are those of the sur-rounding body epithelum ; they lack rhabdites and are approached bynerve fibers from the underlying mesenchyme. The location of theseorgans corresponds to the two light, longitudinal streaks on the sidesof the head seen in the living animal.The testes are of moderate size, numerous, densely packed, andoccupy the dorsal half of the mesenchyme, generally above the intes-tinal branches. They are arranged in two wide areas on both sidesof the midline, extending from the level of the ovaries close to theposterior end.The ovaries, situated at the level of the second pair of branches ofthe anterior intestinal trunk, show no structural peculiarities.The genital pore (pg) leads immediately into two cavities, the maleatrium (am) and, to the right and somewhat posteriorly, the duct of
176 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 103the copiilatory bursa (bd). No common atrium is present,and both the papUla of the penis and the opening of theoviduct are situated in the "male" atrium. The atrium is a conicalcavity, wide anteriorly and tapering toward the genital pore. It islined with a cubical epithelium, below which occurs a thin layer offine circular muscle fibers and a thicker layer of coarser longitudinalfibers.The penis consists of a spherical, muscular bulb and an elongatedpapilla. The penis bulb is differentiated into a wide peripheralmuscular zone and a more central parenchymatic zone which containsa cavity, the seminal vesicle (vs) . The vesicle is lined with a glandu-lar epithelium and its wall forms villuslike projections. The twovasa deferentia (vd) penetrate the penis bulb from the anterolateralsides and open into the seminal vesicle on two prominent conicalpapillae projecting from the anterior wall of the vesicle a short dis-tance from each other.The papilla of the penis is finger-shaped, tapering toward the tip,and is highly muscular. It is covered with a thin cubical epithelium.Below the epithelium there is, in the basal portion of the papilla, athin layer of longitudinal muscles, below which lie a stronger circularlayer and a second longitudinal layer. In the distal part of thepapUla, the external longitudinal layer is lacking. The axis of thepapilla is pierced by the ejaculatory duct (de) which leads from theseminal vesicle to the tip of the papilla. The duct has a cubicalepithelium and a strong coat of longitudinal muscle fibers.The two oviducts approach the midline in the region of the copula-tory apparatus, the right one passing between the atrium and thebursa stalk, and unite behind and above the atrium. The commonoviduct (ode) proceeds ventrally, then curves anteriorly, and emptiesinto the terminal part of the atrium close to the genital pore.The copulatory bm-sa (b) is a lobed sac lined with a tall glandularepithelium. The distal parts of the epithelial cells are filled withfine eosinophilic granules. The duct or stalk of the bursa (bd) is dif-ferentiated into a narrow anterior section with a weak muscular coat,which connects with the bursa, and a posterior wider section whichbends ventrally and opens at the genital pore. The ceUs of theanterior section resemble those of the bursa in having similar granularinclusions. Those of the posterior section lack the inclusions and areciliated. The muscle coat of the duct consists of intermingled longi-tudinal and circular fibers.Taxonomic position.?I have placed the species in the genusDendrocoelopsis established originally for a European species, D.spinosipenis (Kenk). The original definition of the genus was basedon the following characters: fibers of the inner muscle zone of the
FRESH-WATER TRICLADS OF ALASKA?^KENK 177pharynx intermingled ; no adenodactyl ; penis papilla developed, penisbulb of simple structure; oviducts unite without embracing bursastalk; zone of testes extending behind the level of the copulatoryorgans; anterior end with subterminal true sucker; eyes not numerous(Kenk, 1930). Subsequently Beauchamp (1932, p. 254) founded anew genus, Amyadenium, with two species, A. vandeli Beauchamp andA. brementi (Beauchamp), both from the Pyrenees. Two morespecies were reported by the same author in later papers, A. chattoniBeauchamp (1949, p. 60), again from the Pyrenees, and A. garmieriBeauchamp (1950, p. 65), from central France. Beauchamp recog-nized the close relation of the new genus to Dendrocoelopsis, but
Figure 23.
?
Dendrocoelopsis piriformis, diagram of the copulatory organs in longitudinalsection, X 60. am, male atrium; b, bursa; bd, bursa stalk; de, ejaculatory duct; o, mouth;ode, common oviduct; pg, genital pore; vd, vas deferens; vs, seminal vesicle.separated it from the latter on accoimt of the absence of a highlycomplex grasping organ, or true sucker (i. e., an adhesive organ sepa-rated from the surrounding mesenchyme by a muscle layer) . Hyman(1935) described a dendrocoelid species from Montana under thename of D. vaginatus. Again the main characters of the speciescoincide with those of D. spinosipenis with the exception of thegrasping organ, which is of a simpler type. The new Alaskan species,D. piriformis, also falls clearly in the vicinity of the species enumer-ated, as does another species, D. alaskensis, the description of whichfollows on p. 178. Within this group of species there is a gradualdifferentiation of the grasping organ, which is absent in D. alaskensis,present as a moderately developed adhesive organ in D. vaginata,D. piriformis, A. brementi, A. vandeli, A. chattoni, and A. garmieri,and as a more highly developed and muscular sucker in D. spinosipenis.A similar wide variation of the structure of the anterior grasping organ
178 PROCEEDINGS OF THE NATIONAL MUSEUM vol. ids
is seen in the genus Dendrocoelum Orsted where, however, true suckersare not known. In general, the taxonomic vahie of adhesive organsin triclads appears to be subordinated to that of other anatomicalstructures. I therefore tentatively modify the definition of thegenus Dendrocoelopsis by omitting the presence of a sucker as ageneric character, to include the species described as Dendrocoelopsisand Amyadenium.Dendrocoelopsis pirijormis differs from the other members of thegenus (in its wider extent) in several characters: It is pigmented,whereas the others lack pigment and appear white; the presence oftwo eyes differentiates it from the three blind species, D. vandeli, D.brementi, and D. garmieri and from the many-eyed D. chattoni; andthe dorsal position of the testes separates it from D. spinosipenis, D.vaginata, D. garmieri, and D. alaskensis. Apart from these most con-spicuous characters, the structure of the male copulatory organ of D.piriformis is distinctive.Holotype.?On five slides, USNM 22334, Moose Creek, on GlennHighway, milepost 186, near Alaska Road Commission camp, Aug.U. 1950.Distribution and Ecology.?Dendrocoelopsis piriformis is a eury-thermic species and inhabits lakes and their outlets in the southernpart of Alaska and also occurs in a lake near Umiat.Long Lake, on Glenn Highway, milepost 85.9, Aug. 11, 1950, clear water,17.8? C. (near bank) ; under stones, several specimens, two of them mature.Lake on Glenn Highway, milepost 88.1, Aug. 11, 1950, water temperaturevarying with depth (near bank, 19? C.) ; under stones, several specimens, onemature.Lake on Glenn Highway, milepost 23.5 (see pi. 8), Aug. 13, 1950, clear water,23.6? C. (near bank) ; several immature specimens.Stream crossing Glenn Highway at milepost 147.2, outlet of Snowshoe Lake,Aug. 14, 1950, moderate current, water somewhat colored, 17.0? C.; one youngspecimen, under a stone.Moose Creek, on Glenn Highway, milepost 186, near Alaska Road Commissioncamp, Aug. 14, 1950, fast, clear stream, 16.2? C; under stones, two mature speci-mens (holotype).Pippin Lake, on Richardson Highway, milepost 84.4, Aug. 15, 1950, shallowwater near bank, 20? C. ; under stones, many specimens, two of them mature.Fresh-water lake near Umiat, collected by P. F. Scholander, Aug. 15, 1948;18 specimens, majority belonging to the plain form, 1 with distinct stripes, 5sexually mature (USNM 23678).Dendrocoelopsis alaskensis, new speciesFigure 24; Plate 6, Figure 4Description.?I had only limited material of this species and noneof the animals was fully mature. The largest specimen measured 20mm. in length and 4 mm. in width.The anterior end is slightly lobed, with a convex frontal margin
U. S. NATIONAL MUSEUM PROCEEDINGS. VOL., 103, PLATE 7
Top: Beaver pond at milepost 62.6 of Richardson Highway, x\laska. Below the beaverdam, Polycelis borealis under stones. Bottom: Stream flowing along Richardson High-way, Alaska, at milepost 26.3. On the undersides of stones, Polycelis borealis.
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 103. PLATE 8
Top: Stream crossing Sieese Highway, Alaska, at milepost 84.0. Habitat of Pkagocatanivea and Dendrocoelopsis alaskensis. Bottom: Lake at milepost 23.5 of Glenn High-way, Alaska. Under stones near bank, Dendrocoelopsis piriformis.
FRESH-WATER TRICLADS OF ALASKA?^KENK 179and a pair of rounded auricles protruding both anteriorly and later-ally. No distinct adhesive or grasping organ is developed. There isa gentle narrowing of the head (neck) behind the auricles. Behindthe head, the width of the body gradually increases until the greatestwidth is reached. The posterior end is bluntly pointed.The body lacks pigment, being white except for the contents ofthe intestine, which may show through the body wall.There are two principal eyes. The distance between them amountsto about one-third the width of the head at the level of the eyes.The distance of each eye from the frontal margin is equal to, orslightly larger than, the distance from the lateral margin. Additional,supernumerary, eyes were seen in a few individuals at short distanceseither anterior or posterior to the principal eyes.The species bears a striking resemblance to a European species,Dendrocoelum nausicaae Schmidt of the Balkan Peninsula. It isgenerally associated with another triclad inhabiting the same streamsin Alaska, Phagocata nivea, from which it may be distinguished byits larger size and by the position of the eyes.A distinct adhesive organ is not seen in living animals. In histologi-cal sections, a transverse band, pierced by numerous openings ofeosinophilic glands, is found below the frontal margin of the head.The nature of the glands and the local differentiation of the epitheliumcorrespond entirely to the structure of the submarginal adhesive zonewhich is seen in this species, as well as in other triclads, bordering thelateral margins of the body. The frontal adhesive area may, therefore,be interpreted as an extension of the lateral adhesive zone. It issomewhat wider than the lateral one and has no muscular differen-tiations such as are typical of true grasping organs. The continuityof the two zones is interrupted by a short gap on each side of thehead below the auricle.The internal muscle zone of the pharynx consists of a layer of inter-mingled circular and longitudinal fibers. This character places thespecies in the family Dendrocoelidae. The anterior intestinal trunkbears a fairly large number, 21 to 24 pairs, of lateral branches, ordiverticula.Of a total of eight individuals of this species at my disposal, fivewere young, two showed primordia of genital structures, and only onehad the principal parts of the reproductive system developed, thoughnot fully differentiated histologically. The description of the genitalorgans, therefore, must be given with certain reservations.The testes are predominantly ventral, situated mainly below thelevel of the intestinal diverticula, occasionally extending fartherdorsally between the diverticula. No clearly recognizable testes wereseen behind the level of the mouth; they may, however, appear there
180 PROCEEDINGS OF THE NATIONAL MUSEUM vol. io3when the animal matures completely. The ovaries are situatedbehind the third or fourth lateral branch of the anterior iatestiualtrunk.The genital pore (pg) leads into an undivided cavity, the genitalatrium (a), which is narrow at the pore and expands anteriorly. Thenarrow posterior part receives the outlet of the copulatory bursa and,anteriorly to it, the opening of the common oviduct.The penis has a fauiy large, spherical bulb and a plump and shortpapilla. The bulb contains a cavity with irregular outline, the seminalvesicle (vs), into which the two vasa deferentia (vd) open separately.The cavity of the bulb continues into the broad papUla and opens atits tip. The bulb has the usual coat of muscle fibers arranged inconcentric layers. The papilla, which projects only little into thegenital atrium, has two muscle layers underlying the outer epithelium,a circular layer and a longitudinal one. No glandular structures aredifferentiated in my specimen.The two oviducts unite, without embracing the bursa duct, dorsallyto the genital atrium. The common oviduct (ode) opens into theposterior, narrow part of the atrium from the dorsal side.The bursa (b) is, in my specimen, a rather small sac with a narrowlumen. The bursa duct (bd) runs posteriorly, above the penis, to alevel behind the genital pore. There it turns abruptly toward theventral side. Its terminal portion is considerably wider than theanterior part of the duct and opens from the posterodorsal side intothe genital atrium close to the genital aperture. In full maturity, thewidened section of the bursa duct probably represents a histologicallydistinct vagina.Taxonomic position.?The systematic relations of Dendrocoelopsisalaskensis are discussed together with those of the preceding species,D. piriformis. D. alaskensis is distinguished from all other speciesof the genus by the lack of a grasping organ.Holotype. On seven slides, USNM 22335, creek crossing ElliotHighway at milepost 31.0, July 24, 1950.Distribution and ecology.?Dendrocoelopsis alaskensis is an inhabitantof cool, fast streams of the White Mountains and usually shares itshabitat with Phagocata nivea. It is a stenothermic and rheophUicspecies.Clear spring and creek on Steese Highway, milepost 82.5, at the Alaska RoadCommission camp, July 21, 1950; one immature specimen, under a stone.Stream crossing Steese Highway at milepost 84.0 (see pi. 8), altitude 2,700feet, July 21, 1950; two immature specimens, under stones, near liver bait.Creek crossing Elliot Highway at milepost 31.0, July 24, 1950, water tempera-ture 3.2? C; under stones, five specimens, two of them with sexual structuresGiolotype)
.
FRESH-WATER TRICLADS OF ALASKA?KENK 181
I I Ia ode pg bdFigure 24.
?
Dendrocoelopsis alaskensis, diagram of the copulatory organs in longitudinalsection, X 70. a, genital atrium; b, bursa; bd, bursa stalk; ode, common oviduct;pg, genital pore; ph, pharynx (extended through the mouth); vd, vas deferens;vs, seminal vesicle. Zoogeographic conclusionsThe occurrence in Alaska of four endemic species of triclads posesseveral interesting questions. It is known that fresh-water tricladsare most abundantly represented in the northern Temperate Zoneand that the number of species declines toward both the Arctic andthe Tropical Zones. The paucity of the triclad fauna at high lati-tudes has frequently been attributed to the effects of glaciation inrather recent geologic time. During the glacial period, when hugeice masses covered great parts of the northern hemisphere, all fresh-water life over wide areas must have vanished. After the glaciershad receded, the areas were gradually repopulated by species enteringthem from adjacent territories. The pattern of distribution offreshwater triclads m Europe shows evidence of a definite successionof species which migrated into the previously glaciated areas in thepostglacial period (cf. Thienemann's 1950 summary of the pertinentliterature)
.
It is well known, however, that the greater part of Alaska wasnot covered with ice in the glacial period. Geologic evidence ofglaciation has been found only in the Brooks Range, the AlaskaRange (and areas south of it), and in small isolated spots in theYukon and Kuskokwim River Valleys while the remaining surfaceof Alaska remained free of ice (cf. Geological Society of America,
182 PROCEEDINGS OF THE NATIONAL MUSEUM vou i031945). We are thus justified in assuming that the fresh-water lifeof Alaska was not completely destroyed even at the peaks of glacia-tion when practically all Canada and a considerable part of theUnited States were covered with ice caps.The Alaskan fresh-water triclads show no close relationships withthe present North American triclad fauna inhabiting the midwestemplains and the eastern and southern areas of the continent. Acomparison with the fauna of the Rocky Mountains is not possibleat present, since the West of the United States and of Canada isalmost unexplored with regard to triclads and to lower aquatic in-vertebrates in general. In any event it appears highly improbablethat Alaska was populated by species migrating to it from the southor east.On the other hand, the relations of the Alaska triclads to thefauna of Eurasia are unmistakable. Though, according to ourpresent knowledge, none of the Alaskan triclads is specifically identi-cal with any Asiatic form, two species, Phagocata nivea and Polycelishorealis, are very closely related to Asiatic species of the same genera.Figure 25 shows the geographic range of the genus Polycelis as itis known at present. The individual dots on the map representeither single records or groups of neighboring localities where speciesof the genus have been found. In interpreting the map it is to bekept in mind that not all geographical areas are equally well mvesti-gated with regard to the occurrence of lower invertebrates. Europe,Japan, and the eastern parts of the United States are comparativelywell known while our knowledge of the Asiatic, Western American,and African triclads is still rather deficient. A study of the mapsuggests that Polycelis is primarily a Eurasian genus. It appearsto have extended its range, in some earlier geological period, to thenorthern rim of Africa.* In a similar way it may have migrated intoAlaska at the time of the cenozoic land bridges and may have pene-trated south along the Rocky Mountains. It is highly probablethat Polycelis will be found, in the future, more widely distributedin the Rockies than present collection records indicate.The repeated emergence of a land bridge between Alaska and theeastern tip of Siberia is generally accepted by geologists and paleon-tologists. There is ample evidence of an exchange of faunal elementsbetween the two continents (cf. Simpson, 1940 and 1947). The mostrecent corridor must have existed during the glacial stages of thePleistocene. The volume of ice masses accumulated over vast areasof the northern hemisphere has been estimated conservatively at34 to 42 million cubic kilometers. The corresponding depletion ofThe presence of Polycelis oculi-marginata (Palombi) in New Guinea is a zoogeographic enigma (cf. Beau-champ, 1947).
FRESH-WATER TRICLADS OF ALASKA?KENK 183
fe
184 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 103the ocean must have lowered the sea level 50 to 90 meters below thepresent level (Daly, 1934, pp. 41-50). The depth of the eastern partof the Bering Sea (withm the peruneter passing through the easternprojection of Siberia, the Seward Peninsula of Alaska, and Nunivakand St. Lawrence Islands) averages less than 40 meters. Thus theocean bottom between Alaska and Asia must have emerged with eachglacial stage, forming a wide connection between the two continents.This process may have been enhanced by the uplifting of the areaalong the margin of the ice cap, brought about by plastic or elasticdeformation of the earth crust under the weight of the ice masses.A land bridge between Alaska and Asia must have persisted forprolonged periods of time. Simultaneously, Alaska was discon-nected from other inhabitable areas of North America by broad icefields.In view of the geological history of Alaska we may conclude thatthe present Alaskan fresh-water triclads are the remnants or successorsof triclads that lived in Alaska in the glacial times and perhaps evenin preglacial periods, and that they are, in all probability, of Asiaticorigin. It may further be assumed that some Alaskan triclads haveextended their range during the postglacial period and proceededsoutheast along the Rocky Mountains.^ The occurrence of a speciesof Polycelis in Wyoming and South Dakota may have resulted fromthis migration. More light would be thrown on this question by amore thorough study of the triclad fauna of the Canadian andAmerican Rockies. Literature citedArndt, Waltheb1922. Untersuchungen an Bachtricladen. Ein Beitrag zur Kenntnis derPaludicolen Korsikas, Rumaniens und Sibiriens. Zeitschr. fur wiss.Zool., vol. 120, pp. 98-146, pi. 4.Bazikalova, a. fA.1947. Turbellaria-Triclada vostochnol Sibiri i Pribalkal'fa. Doklady Akad.Nauk SSSR, new ser., vol. 55, pp. 671-672.Beauchamp, Paul be1932. Biospeologica. LVI. Turbellaries, Hirudinees, Branchiobdellidfe.Deuxifeme s^rie. Arch. Zool. Exp^r. et Gen., vol. 73, pp. 113-380,pis. 6-8.1939. La syst^matique et I'^thologie des Fonticola (Turb. Triclades). VgstnfkCeskoslov. Zool. Spolecnosti v Praze, vol. 6-7, pp. 91-96.1947. Observations sur quelques Turbellaries du Mus6e royal d'Histoirenaturelle de Belgique. Bull. Mus. Roy. Hist. Nat. Belgique, vol.23, No. 33, 11 pp.1949. Biospeologica. LXIX. Turbellaries (troisifeme s^rie). Arch. Zool.Exp^r. et G6n., vol. 86, Notes et Revue, pp. 50-65.1950. Nouvelles diagnoses de triclades obscuricoles. Bull. Soc. Zool. France,vol. 75, pp. 65-70.
? I wish here to correct my assumption in a previous paper (Kent, 1943, p. 6) that all Canadian tricladshad entered Canada from the south.
FRESH-WATER TRICLADS OF ALASKA?^KENK 185Bergendal, D.1890. Studien iiber nordische Turbellarien und Nemertinen. Ofv. Vet.-Akad. Forh., 1890, pp. 323-328.Daly, Reginald Aldworth1934. The changing world of the ice age. xxi+ 271 pp., 6 pis. New Haven.Geological Society of America1945. Glacial map of North America. Special Papers, No. 60.Girard, Charles1894. Recherches sur les Planari^s et les N^mertines de I'Amerique du Nord.Ann. Sci. Nat., ser. 7 (Zool.), vol. 15, pp. 145-310, pis. 3-6.Hyman, Libbie H.1931. Studies on the morphology, taxonomy, and distribution of NorthAmerican triclad Turbellaria. III. On Polycelis coronata (Girard).Trans. Amer. Micr. Soc, vol. 50, pp. 124-135.1934. Report on triclad Turbellaria from Indian Tibet. Mem. ConnecticutAcad. Arts Sci., vol. 10, No. 2, pp. 5-12, pis. 1-2.1935. Studies on the morphology, taxonomy, and distribution of NorthAmerican triclad Turbellaria. VI. A new dendrocoelid fromMontana, Dendrocoelopsis vaginatus n. sp. Trans. Amer. Micr.Soc, vol. 54, pp. 338-345.1937. Studies on the morphology, taxonomy, and distribution of NorthAmerican triclad Turbellaria. VII. The two species confusedunder the name Phagocata gracilis, the validity of the generic namePhagocata Leidy 1847, and its priority over Fonticola Komdrek 1926.Trans. Amer. Micr. Soc, vol. 56, pp. 298-310.Ijima, I., and Kaburaki, T.1916. Preliminary descriptions of some Japanese triclads. Annot. Zool.Japon., vol. 9, pp. 153-171.Kaburaki, Tokio1922. On some Japanese freshwater triclads; with a note on the parallelismin their distribution in Europe and Japan. Journ. Coll. Sci., Imp.Univ. Tokyo, vol. 44, No. 2, 71 pp., 1 pi.Kenk, Roman1930. Beitrage zum System der Probursalier (Tricladida paludicola). III.Zool. Anz., vol. 89, pp. 289-302.1936. Bemerkung zur Trikladenfauna Turkestans. Zool. Anz., vol. 115,pp. 76-80.1943. Notes on the planarian fauna of Canada. Canadian Field-Nat.,vol 57, pp. 5-6.LivANov, N. A., and Zabusova, Z. I.1940. Planarii basselna Teletskogo ozera i novye dannye o nekotorykhdrugikh sibirskikh vidakh (Paludicoles du Lac Teletzkoe et nouvellesdonnees sur quelques formes sib^riennes) . Trudy Obshch. Estes-tvoisp. pri Kazan. Univ., vol. 56, pp. 83-159.MuTH, Anton1912. Beitrage zur Kenntnis der Gattung Sorocelis Grube. Mitt. Naturw.Ver. Steiermark, vol. 48, pp. 381-410.Palombi, a.1931. Turbellari della Nuova Guinea. In: R^sultats scientifiques duvoyage aux Indes Orientales Neerlandaises de LL. AA. RR. lePrince et la Princesse Leopold de Belgique, vol. 2, No. 8, 14 pp.,1 pi. (M6m. Mus. Roy. Hist. Nat. Belgique, hors s6ne).
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