12.-PRELIMINARY REPORT UPON THE INVERTEBRATE ANIMALS INHABITING LAKES GENEVA AND MENDOTA, WISCONSIN, WITH AN ACCOUNT OF THE FISH EPIDEMIC IN LAKE MENDOTA IN 1884. BY S. A. FORBES. LAKE GENEVA. My first visit to Lake Geneva was rnadu in October! 1881, a6 an incident of work in progress on the Illinois State Natural History Survey, my purpose at the time being to compare the invertebrate fiune and tho biological couditions of that lake with those of the much smaller and shallower lakes of the same series in northeastern Illinois. On this visit I hauled t h e dredge aud beam-trawl and the surface net re- peatedly in several parts of the lake, both along shore and in the deepest water, and carefully worked the product of the dredge and trawl through a set of assorting sieves, saving in alcohol everything collected. In August, 1887, 1 improved the op- portunity of a casual visit to this lako to make inuch larger collections witLh the sur- face net, ran several lines of soundings across the lake, and collected from deep water, for analysis, the peculiar, soft, fine, mud-largely a chemical precipitate-which covers the bottom there to a great depth.” * This mud has a peculiar rank, dniost offensive, odor, and a soft, greasy feel, and rubs away largely between the fingers. It is of a pale slate-blue color when dry, darker when moist. Under the micro- scope it has a semi-crystalline appearance, and contains very little vegetable d6bris and uot much Band. It effervesoes freely in sulphurio aoid, but does not wholly dissolve. A sample of this mud which had been taken from a depth of 20 fathoms was submitted to Prof. William McMurtrie, of the cheniical department of the University of Illinois, who reported upon i t as follows: The following are the results of analysis of lake mud : Por conk Carbon dioxide ( COZ). ................................................. g5.00 Caloium oxide ( CHO 1.. .................................................. 27.13 Magnesium oxide (MgO ) ................................................. 3.65 Organic matter. ......................................................... 4.80 Insoluble residue.. ...................................................... 38.20 Ferrio oxide ( Fe2 Oa )-. .................................................. 1.50 Aluminio oxide ( Ala O3 ) .................................................. 4.67 Calcium carbonate ( CaCo3 ) .......................................... 48.445 Magnesium carbonate ( MgCOs ) ......................................... 7.665 Ferrio oxide ( Fea O3 ). .................................................. 1.500 Aluniinio oxide ( Ala O3 ). ................................................ 4.670 Organio matters.. ....................................................... 4.800 Iu~olubh3 residue ........................................................ 32.200 “These are doubtless engaged in combination as follows: ’‘ The insoluble residue cousists of clag and sand.” 473 474 BULLETIN O F THE UNITED STATES FISH COMMISSION. Lake Geneva, in Walworth County, Wisconsin, is a clear and beautiful sheet of mater about 7 miles long by 19 in greatest width, with a n extreme depth, according to my soundings, of 132 feet. It is a glacial lake, lying in a trough-like valley of the drift, the southern side of which formed part of the terminal moraine of the great Lake Michigan glacier. The valley is continued westward with a very gradual rise beyond the head of the lake, where a small stream empties its clear, cool water. By way of the outlet ateits eastern end, its waters pass through Fox River into the Illinois. Its banks are high and rolling, but nowhere blufty, and there is no rock anywherein sight. The slopes of the bottom are mostly gradual, but off the “points” they may reach, for the first 500 or 600 feet, a descent of 1 foot in 5 ; while in the bays this is only about 1 in 50.* The vegetation of this lake is chiefly confiued to a narrow belt along the shore, except in Williamd Bay on the north side and in t h e shallow water near the outlet. In the deepest parts the bottom is perfectly deRtitute of living plants higher than diatoms, and there is also a remarkable scarcity and small variety of animal life in this situation. In the shallow water, from the shore to a depth of 5 fathoms, the most abundant plants observed in 1881 were as follows : Myriophyllum hetsrophyllum, M . scabratam, Ceratophyllum demerszcm, Potamogeton compressum, P. luoms, P. pauci$orum, Anacharis canaciensi8, a?ha &ara c0ntraria.t Swimming and creeping among the somewhat scanty growth of these aquatic plants, wa8 a small variety of animals, the most abundant of which were the smallest of our common amphipod crustaceans ( Allorchestes dentata Smith) and the larvae of an abundant genus of gnats-Chirononzzcs. A partial examination of the material col- lected by a dozen hauls of the dredge in this shallow water gave me the following imperfect list : SHALLOW WATER COLLECTIONS, 1881. 4 INSECTA. 1. Pavaponyz sp.? An iuterestiug aquatih caterpillar, ribhly provided with tnfted tracheal gills on all surfaces of the body, probably belongs to this genus of pyralid Lepidoptera. Two examples were taken among weeds growing on a gravelly bottom, in water 6 feet deep. Several adult specimens of this beetle were taken in a haul along shore, . 2. Stenelmis orenabs Say. doubtless from the aquatic weeds. 3. Dytisoidm. A single larva. 4. C/&wmnw sp. Very many specimens of small white la rva belonging to undetermined species of 5. Plvryganeidm. Various caaeworms, mostly Leptocerida, with sand tubes, either straight and slender Tubes sometimes made of o webbed membrane covered with a thick layer A remarkable larva of Lage- A these very abundant gnats. or short and curved. of small spherical colonies of Rivularia or other similar Alga. nopeyche frequently occurred, the case transp arent and commonly oovered with diatoms. single specimen of SericoRtomida. G. Agrionha and Libellulina. Nymphs of dragon flies. 7. Ephemeri&. Most oommonly nymphs of Cumis, of an undetermined speoies. CRUSTACEA. 8. Cambarus virilie Hagen. Cray-5shes were not. at all abundant in this lake, but a few young speci- mens of this species were taken in the dredge. * See profiles, page 476. t Determined for me by Prof. T. J. Burrill, of the Univereity of Illinoia LAKE GENEVA - WISCONSIN - INVERTEBRATES OF LAKES GENEVA AND MENDOTA. 475 9. IO. 11. Gammarua fasdatua 8ay. d~~orchestes dentata (Smith) Faxon. among the W e e i h Candona elongata 9 Herrick. This shelled entomostracan occurred but Once in the dredge. occasional examples occurred. This was by far the commonest Crustacean, and swarmed MOLLUSCA. The common mollusks from my dredgings were Unio luteolus and Anodonta footi- ana (neither abundant), Planorbis campa&ata and other species of that genus, €'hi- dium adamsi Pr.," P. comprensurn,t Sphmrium solidulum,t a few Physas and Limnem (the former the commoner), an occasional Melantho, a great number of Amnioola cin- cinnatiensis, and many examples of Valvata tricarinata and V. sincera. V IC R M E 8. The worms of these inshore collections were limited to a few leeches and plana- rians, occasional specimens of Stylaria lacustris Linn., and an uiidetermined species of Pristina. Besides the foregoing, I obtained here only a small number of water-spiders (Hgdrachnidae), a few examples of our most abundant darter (Boleosoma nigrurn), and R common sunfish (Lepomis). ' DEEP WATER COLLECTIONS, I66l.t In the deeper water the collections were not especially different where the bottom was covered with vegetation. A haul of the beam-trawl made on a mud bottom in the eastern end of the lake a t a depth of 12 fathoms, among Ceratophyllum and Ana- charis, gave a nearly full assortment of the smaller mollusks of tho lake (Valvata tri- carinata, V. sineera, Amnioola oincinnatiensis, Planorbis, Physa, 8plmrium solidulum,. Pisidium adamsi, and P. compressum), Physa, Sphcerizcm, and Valvata sineera being the most abundant. Number8 of Chironomus larvae, a dytiscid larva, and a caseworm were the only insects,.and Allorohestes and Candona the crustaceans of the haul. Among the Vermes was a long and slender species (Limnodrilus) with four rows of notohed or forked setae arranged in short, transverse, comb-like ranks, each of four to six. A short haul of the dredge a t a depth of 15 fathoms in Williams' Bay, on a bot- tom of sandy mud covered with dvad leaves, yielded a siugle Physa, a small Plumor- bis, a multitude of Pisidium adarnsi, many Valvata stpiatella, many larvae of Uhirono- mus and pupae and pupa cases of Corethra, a few Candona elongata, a multitude of dead branches of a polyzoaxl (apparently Bedrdcella), many Limnodrilus, and a few examples of Btylaria lacustris. The more highly organized crustaceaus and insect larva were here altogether wanting, the princ2pal animals being the smaller mollusks, Pisidium aud Valvata, the wormlike larvae of gnats, and the slender, reddish worm, Limnodrilus, living in the slime. A single haul on a mud bottom near the eastern end of the lake, at 19 to 20 fathoms, gave only large red Chironomus larvs in considerable numbers, several . _ - *Determined by Mr. E, A. Pilsbry, of tchc Philadelphia Academy of fjcienoes. t Named by comparison with specimens determined by Mr. G. W. Tryon. t For the opportunity to dredge this lake to advantage I was greatly indebted to Mr. N. K. Fair- bank, of Chicago, who plaoed at my disposal for this purpose his stem-yaoht and its crew. 476 BULLETIN OF THE UNITED STATES FISH COMMISSION. examples of Pisidium adamsi a single Gammarus fasciatus (doubtless taken in lift- ing the dredge), and one dead shell of Planorbis campanulatus. Finally, two hauls of the trawl and two of the dredge in the middle of the lake, at a depth of 23 fathoms, yielded quantities of the softest black mud with some admixture of dead leaves, an abundance of large red Chironomus larva, Pisidium adamsi, and the undetermined worm (Limnodrilus) already mentioned. The only other specimens secured by this deep-water work (which aggregated over a mile of continuous hauling) were two specimens of Sphmrium, one of Valvata trioarinata, one of V. siacera, a dead Physa, a few pupae of Corethra, and three leeches. No living vegetation was found here except diatoms. With the surface net, in open water, I secured at this t ime only a moderate num- ber of a Daphnia closely resembling D. retrocurva Forbes (and possibly a variety of that species), a few examples of Epischum lncustris Forbes, a Diaptomus (apparently a variety of sicilis), another large copepod, Limnocalanus macrurus, and the remark- able cladoceran form, Lqtodora hyalina. The material of 1887 was obtained mostly with a towing net, in eighteen collec- tions, made at various points dong the margin in shallow water and also in the deep- est parts of the lake, The following lists, although not exhaustive, are sufflciently complete to show the dominant and associate species, and the conditions governing their relative abundance. DEEP-WATER COLLECTIONS, 1887. Upper end of lake, August 6, deep water, clear weather, sunrise, wind. A surface haul and a small collection, with much small vegetable drift. 1. Larva o f Cliironon~ua. 2. Young neuropterous larva. 3. A large hydrachnid, undetermined. 4. A.?k~OheEte8 denlata Faxon. 5. Daphnia retrocurva, var. 6. Daphnella brachyura. 8 7 . Sida cryalallina. 9. Epischura laoustris Several specimens August 5, deep water, at surface, sunset, calm. A small collection, obtained by dragging the A few specimens. A few females bearing egge. An occasional specimen. 8. cYC~?0p8, p. towing net behind a steamer. 1. Daphnia retrocurva, var. 2. Epiachnra laoustria. The principal part of the collection. 1. Chironomus. 2. Daphnia retrocurva, vm. The greater part of the collection. 3. Epischura laoustria. Several specimens. 4. Diaptornue sioilia, var. A few examples. August 5, deep water, 10 a. m., at surface, cloudy, calm. A few examples of larva and pupa. A small collection. August 9, deep water (20 fathoms), 10 a. m., sunshine, net hauled about 10 feet below surface. A large collection. 1. Leptodora hyalina. Several specimeue. 2. Daphniaretroourma, Tar. The greater part of the collection. 3. Daphnella bi achyura. A few examples. 4. Cyolop~, sp. A few examples. 5. Epischura laoustria. A few examples. 6. Diaptomue SiCili8 and var. A few. INVERTEBRATES OF LAKES GENEVA AND MENDOTA. 47 7 August 9, deep-water, 4 p. m. sunlight, uet hauled about 20 feet below surface. A good 001- lection. 1. Leptodora hyalina. Several. 2, Daphnia retrocurva, Tar. A great nnniber. 3. Daphnella brachyura. Occasional specimens. 4. Cyolops, sp. Very few. 5. Epiachura laoustrfs. Very abundant. F . Diaptornus sicilis, var. An occasional example. August 9, 10 a. m., sunshine, deep water, calm; net dragged about 90 feet below the surface. Avery I ; i rge collection. 1. Leptoclora hyalina. A great number. %. Daphnia retroourva, var., with obtuse apcx to helmet. A very large number. 3. Episohura laouetris. Occasionally scen. 4. Diaptomua sioilis, Tar. 1. Leptodora hyalina. A few. 2. Daphnia retrocurva, var. The main par t of the haul. 3. Episolura laoustria. 4. Diaptomue iniperfeotua. 1. Daphnia retroourva, var. Many exaniples. 2. Daphnclla braclhyura. Occasional young. 3. Epieoliura lawstria. The principal part of the catch. August 7, upper end of lake, deep water, 9 p. m., at ~nrface, stiff breeze. A large collection. 1. Leptodora hyalina. Ocoasionally observed. 2. Daphnia retrowrva, var. The greater part of the collection. Females were bearing cgga and young in various stages of development, the gerruiual disk just forming in some, and otliers nearly ready to leave the brood cavity. The fernale nsuitlly carries but a single egg. These Daphnias were feeding on unicelluler Algw, as shown by crushing specimens on a slidc. Not abundant. One female noticed bearing spermatophore. August 9, deep water, 4 p. m., 10 feet below surface, sunshine, calm. A good collection. A few examples. August 4, upper end of lake, deep water, 9 p. m., moonlight, at surface. Fine and large eollectiou. A few examples. 3. Daphnella brachyura. A few young examples. ' 4, Episohura laoustris. Many specimens. One male seen with a slender spermatophore partly 5. Diaptomus eioil.is. Occasional specimens. A repetit,iou of the foregoing. 1. Leptodora hyalina. A half-grown example. 2, Daphnia relroourva. Only occasionally seen. 3. Episohura lawetria. This collection consisted almost wholly of this speoies. Evidently breeding liere rapidly, the ovaries containing ova, as many as ten to fifteen in each female, and the abdomens of all having the spermatophore attached. Many of the ova had a large, central, orange globule, and floated when detached. Most of the males with developed spermatophores. 4. Diaptomus sioilis, var. Several specimens .8 to .Qmm long. Males with well developed sperma- tophores. A single short haul of the towing net in the mud of the bottom, at a depth of 10 fathoms, yielded several specimens of Pisicliunl adamsi (the characteristic deep-water mollusk of this lake), au occasional Daphnia retroourva var., several cyprids (including Candona elongata), a few duad branches of Polyzoa (apparently Fmdrioolla), and a single Limnodrilus-the common mud-worm of the interior of the lake. extruded. SHALLOW-WATER COLLECTIONS, 1887. Several collections made from the margin of the lake to a depth of 9 or 10 feet gave a much mor6 miscellaneous list than those from the open water. I . Corethra. Pupa. 2. Chirononaus. Larvw and puprs, the formor ocourring in every haul. 478 BULLETIN O F THE UNITED BTATES FISH COMMISSION. 3. Ephemeridm. Nymphs of several species, not determined. Most commonly belonging to the genus Ccenia; one example closely allied to Ecdyurua, and undoubtedly of that group by Eaton's Monograph ; another similarly related to Ephemerella. 4. Phryganeidm. Undetermined larva. 5. Hydraohnidm, sp. 6. Allorohestea dentata. Abundant, especially among the weeds. 7.' Alona, sp. Sevfral times occurring. One allied to A . tuberoulata Koch, but probably dis- tinct. 8. Acroperua leuwoephalua. Noticed but once. 9. Eurycerczca lamellatus. More abundant. 10. Ophryozus grauilia (?) Bars. Examples of a specie8 of this genus not distinguishable from gracilis a8 described by Sars* were obtained among weeds in water 6 to 9 feet deep. This i s apparently identical with Lyncodaphnia macrothroidea Herrick. 11. Daphnia retroeurva, var. 12. Moina rectiroatria. 13. Latona aetifera. Three specimens of this somewhat rare crustacean were taken among 14. Sida oryatallina. Rather abundant in our collections. 15. CyoZopa, sp. 16. Epischura laouatris. Only a few examples in one of the hauls at the margin. 17. Diaptomua aioilis, var. A few specimens among weeds, in water 9 feet deep. 18. Stylaria Zacuatria. 19. Ophrydium, sp. A few colonies of this protozoan taken from the.weeda along shore. 20. Aroella, sp. Taken as above. 21. Diflugia, sp. Only a single specimen. Taken at the margin. weeds in water 6 feet deep. Several specimens ; not cntically studied. A single example near the margin. Taken as above. August 5, among the weeds at outlet, 5 p. m., sun, wind. 1. Chironomua, larva. 2. Agrionina. 3. Ephemsridm. Fig. 18.) 4. Hydraohnida?. Four specimens taken. 5. Allorcheatea.dentata. Not abundant. 6. Cyprididm, sp. Several examples, ainong them representatives of Cypria vidua. 7 . Euryoeroua lamellatus. Several specimeus. 8. Sintocephalus, sp. A dozen specimens similar t o americanua,but differing apparently in speci- fic characters. 9. Moina reotiroatria. Two examples. 10. Daphnella brachyura. 11. Sida oryatallina. A few. 12. Cyclope pectinifer Cragin. 13. Epiachura laoustria. A large number of this species, making, in fact, the chief contents of 14. Diaptomus aioilia, var. A few examples. Two or three examples. A single larva of these dragon flies. Severai larvm, mostly of the Ephemerellagroup. (Eaton'rr Monograph, P1.40, Several examples, including young the collehtion. August8, upper end of lake, sandy bottom, with Ghara aontraria. 1. Chironomua, lrtrvm. A slender white species. 2. Ccenia, sp. A single larva. 3. Allorelteatea dentata. Several examples. 4. Leptodora hyalina. Several examples. 5. Aoroperua leucooephalua. 6. Ophryoxua gracilis ( 1 ) . Three examples. 7. Daphnia retroourva. A very few. 8. Latona aetifera. A singlc specimen. 9. Sida orptallina. Several examples. * Oversigt af de Omgegnen af Christiania iagtcagne Crustacea cladocera. Forhandlinger i Videns- kabs-Selskabet i Christiania, 1861, p. 158. INVERTEBRATES OF LAKES GENEVA AND MENDOTA. 479 10. Epieohwa lacustris. A very few. 11. Diaptomus gracilis. Only one Specimen. 12. Ophrydiunt, sp. A single colony. A haul of the towing-net in swift water at the mouthof the inlet, made at 9 p. m., gave the follow- ing list : 1. Corethra, sp. A few pupa about ready to emerge. 2. Corixa, sp. Several young. 3. Ephmeridm. The collection was largely composed of larva of this family, mostly of the genus Camis. One dissected, had filled the alimentary canal with fine dirt, containing a fow fila- menbsof Alga and occasional diatoms. Other larva were allied to Callibmtis of Eaton’s Men- ograph. The palpi of the firat and second maxilla had, however, but two joints eaah. One ally of Ecdyurus was also noticed. 4. Eydraohnidm. Several examples. 5. Alloroheste8 dentata. A single one. 6. Daphnia retrocurva, var. A few. 7. Sida erystallina. Several examples. 8. Cy:ycEops, sp. Occasional examples ; not determinod.’ 9. Epischura laaustris. Several specimens. 10. Limnodrilue sp. A single specimen of this mud worm. A small collection made by turning stones in the water along the shore gave sev- eral I m w of Psephenus, probably lecontei, but differing noticeably from Eellicott’s figure of that curious and interesting animal, as given in the 6‘ Oanadian Entomologist,” Vol. xv., p. 191. A O’cenis nymph, another of the Ecdyurus group, and a phryganeid pupa in its sand tube, were the only other insects. A single fresh-water shrimp (Palwmonetes exilipes) was taken here, together with a few examples of Bammarus-possibly young of f a h a t u s , but too small for determination. Also Allorchestes dentata, a single Bor- d im, and several small leeches. It is evident from the foregoing that even in a lake of so moderate size a8 this, the smaller inhabitants are quite clearly divided into pelagic and littoral groups, the lat- ter contairiing the greater number of species, but the former not less numerous in in- dividuals; and a comparison of the results of dredgings shows that this difference ap- plies to the animals of the bottom as well as to those swimming freely above it. This pelagic group of Entomostraca includes Leptodora hyalina, Daphnia retroourva, and Episohura lacustris, as its principal species, Diaptomus sicilis, another pelagic form, being, apparently, not very abundant in this litke ; while the characteristic animals of the bottom of the interior parts of tho lake are Pisidiwm adamsi, a large red ~hironomus , larva, atid a species of Limnodrilus-both this worm and the larva ju s t mentioned making tubular burrows in the mud. It is also apparent from the product of the towing net in deep water under varying conditions, tihot the pelagic Entomovtraca avoid the surface by day, whether it be rough or calm, or the weather cloudy or clear ; but that they do not necessarily withdraw to any gwat depth-hauls 10 feet below yielding ‘‘ good” or “large” collections when the sun was shining. By night, on the other hand, the yield at the surface was large, even in a high wind. LAKE MENDOTA. I first visited LakeMendota in August, 1889, at therequest of Prof. S. F. Baird, U. 8. Uommissioner of Fish and Fisheries, for the purpose of making a study of a most remarkable mortality among the fishes of a single species in the lake-the common perch (Perca jlavesoens Mitch.). 480 BULLETIN OF THE UNITED STATES FISH COMMISSION. In August, 1885, I returned, again at Professor Baird’s request, with Prof. H. Gar- man, then my assistant, for some further studies bearing on the same subject. Fourth Lake, or Lake Mendota, Wisconsin, is the uppermost and largest of a chain of lovely glacial lakes lyiug about the State capital, finding an outlet through a small stream into Rock River. It measures about 5$ miles in greatest length, from east to west, and about.3& in width, from ‘6 University Landing” to the head of Oat- fish Bay. It is thus wider than Lake Geneva, but not so long, and is not nearly so deep. The deepest sounding made by me was but 79 feet, and the average of six soundings, well distributed over the trough of the lake, was 10 feet less. The bottom is morediversified than that of Lake Geneva, showing reefs of rock and of sand, and a large area of weedy shallows. Its waters consequently swarm with fish-especially with the common perch-and the amount and variety of invertebrate life is doubtless greater than in the more uniform Lake Gene.-a. The bottom in the deeper water is not different in character from that of the other iake, bu t is covered by the same soft cal- careous mud, with its peculiar little group of animal inhabitants. Catfish Bay, about a mile and a half across, and half as deep, is bordered by an ex- tensive marsh, which is drained by Catfish Ureek, the principal feeder of the lake, There are about 80 acres of marsh at other points around the lake, but the shores are otherwise rolling, or even bluffy, especially in the narrower and deeper eastern division of the lake; and here are also several unfailing springs. Many other springs are said to open along the shores, below the water.leve1. This lake differs from the others of the chain by the fact that i t has much the largest drainage area and receives a larger affluent than any other; and this, as already said, drains a swamp. The waters of the lower lakes come mostly from Lake Mendota, in which they must have depos- ited much of their sediment, and where much of their organic matter must nndergo decomposition before they flow off through its outlet. On the other hand, about three-fourths of the sewage of the city goes into Third Lake, or Lake Wenona, the next below. DREDGINGB. My general collections from the lake in 1884 were limited, by want of time, to thre’e hauls of the dredge, made with the aid of a smell steamer, one in shallow water (8 to 9 feet) on a sandy bottom, one on a; rocky reef a t a depth of 12 to 18 feet, and a third on a mud bottom at 12 to 12& fathoms. The first haul, on a sandy bottom covered with Nitella, yielded a great number of small white larva: of Ohironomus, with several small amphipod crustaceaus (Allor- ohestes &ntata), two or three small mollusks (Amnicola), a few worms (Stylaria Zacustris), a single larval ephemerid (Omnis), and two Entomostraca (Zurycercus Zumel- latus aud a species of Oypris.) The collection was a small one, the entire product tt cubic half-inch. The haul on a rocky bottom gave only some small mollusks, not yet identified. The deep-water dredging gave precisely the same group of animal forms as those in the mud of Lake Geneva, namely, a good collection of Pisidium adamsi Pr., several large deep red Ohironomus larva, and a species of the tube-making worm Limnodrilus. The principal collections of 1885 were made by nine hauls of the dredge, three of a fine-meshed seine, and seven of the surface net. Those from the deeper water did not differ in auy way from those of the preceding , white House I I I _.,I. sl,- * J-caze gme.9 I N S A N C A 5 Y L U Y 0 MAP O F LAKE: MENDOTA WISCONSIN catfish ~a~ S H A L L O W F L A T n, Asylum B a y INVERTEBRATES OF LAKES GENEVA AND MENDOTA. 48 1 year; but a haul in only 20 feet of water on the rocky reef above mentioned gave the common deep-water forms, Pisidium adamsi and the red Clbironomus,* with an occa- sional Corethra larva also. The shallow-water dredgings of 1885 were much more fruitful than those of 1884, giving many times the number of individuals, and especially a greater number of case- worms and small crustaceans (Allorchestes). A cursory examination of a haul of4he dredge made on the sandy shallow, likewise dredged in 1884, showed an abundance of Allorchestes dentata and small white Chiro- nomus larvae, a multitude of cam-worms of various genera (including the curious Hsliopsyche in its spiral tube of sand grains), Amnicola, Valvata tricarinata and V. sincera, Sphccrium, leeches, planarians, etc., aud a few Entomostraca. A fine Plzcma- tella occasionally occurred encrusting the stems of weeds in shallow water. The ordinary Unionidae of these waters were Unio luteolus and Anodonta footiana, both of which were very abundant. I n the surface net occurred immense quantities of a helmeted Daphnia with head of truly monstrous size, sometimes larger than the body, apparently the Daphnia kerusses of Cox, rather imperfectly described and figured t from Fox River, the general out- let of this chain of lakes. With this were also many Daphnias of a species appar- ently new. Associated with these were frequently found large numbers of Lqto - dora hyalina, a few Oyclops, Diaptomus, and Epischura, occasional larvae of Ohirono- mus and Oorethra,$ examples of Daphnella and of water-mites (Hydrachnidae), and immense and astonishing quantities of a shelled flagellate infusorian, Ceratiurn longi- corne, with now and then the curiously similar rotifer, Anurea longispinu. These mi- nute forms fairly lined the net, and clouded the alcohol in whioh the specimens were preserved. If any useful comparison of the biological conditions prevailing in Lake Mendota during these two Years may be made on the rather slender basis of my collections, it would lead to an inference that invertebrate life was very much more abundant in 1886 than in 1884, and would suggest an over.population of the lake in the latter y e k which had greatly reduced the Usual food Of fishes of indiscriminate carnivorous habit. The vast abundance Of the Perch especially, in this lake, is shown by the fact that they formed nearly the whole product of three hauls made with the seine in 1885, not- withstanding that approximately 300 tons Of this species had died here during the epidemic of the year before. *This blood-red larva, so Often mentioned, is uniformly segmented, and about 30 millimeters long. It bears on the back of the penultimate Segment four clavate anal appendages about as long as the segment itself, and on the antepenultimate segment two pairs of similar appendages, one at theanterior third and the other et the posterior margin. At the posterior margin of the dorsal surface of the penultimate segment are two prominent chitinous tubercles,, each beering three long reourved hairs. The labrum bears fifteen teeth, the middle one large and blunt with a very smsll coherent tooth eaoh side. The remaining six on each side diminish in size outw&rds, the inner one of the series being larger than the median tooth. This tooth and the seoond are verr olosely united, the others free. The antenna, are five-jointed ; the first joint cylindrical, stout, and very long, more than twice a8 long as the other four taken together. It bears articulated to its inner distal margin a long spine, lobed at the base, and as long as the remainder of tho antenna, The next joint is also oylindrical, and about one-fifth as long as the first; the third joint is thiok and short; the fourth longer but more slender; aud the last minute. t Amer. Monthly Micros. Jour., Vol. IV (1883), p. 88. $ Our collections were all made by day. Bull. U. 5. I?. C., 88-431 482 BULLETIN OF THE UNITED STATES FISH COMMISSION. THE FISH EPIDEMIC IN LAKE MENDOTA IN 1884. Early in July, 1884, public attention was attracted, a t Madison, Wisconsin, to the extraordinary numbers of fishes dying and floating ashore in Fourth Lake or Lake Mendota. By the middle of the month the accumulation of their rotting bodies along shore had become a public nuisance, and the street commissioner began to cart them away from the city front and bury them. By the 19th not less than 16 tons had been thus removed, and by August 4 from 76 to 100 tons. As the city borders only a small part of the lake, i t was estimated that fully 300 tons had died up to that time, On August 7, the Madison Transcript reported that 200 tons had been hauled away by the city authorities during the four weeks preceding, and that the fishes were still dying. Angust 16, when the writer arrived a t the lake, this remarkable epidemic had practically ceased, and during the week following (about six or seven weeks after its beginning) it disappeared completely, not to return that season or the following summer. By far the greater part (perhaps 90 per cent.) of the fishes which perished were the common perch (Peroa jZavescens), much the most abundant species in the lake. Next came the lake herring (Coregonus artedi)," locally called the "white fish jr7 while pike-perch, white bass, and sunfish (Ltpomis) were much less numerously represented. My own first visit to the lake was made in cossequence of a request from Professor Baird, then U. 5. PiRh Commissioner, conveyed in the following letter received by me at Normal, Illinois, August 13: WOOD'S ROLL, MASSACHUSETTB, Augu8t 10, 1884. DEAR SIR: Would it be convenient for you to visit the distriats in Wisconsin where the mortality among the fish has developed itself to a very great degree 0 If you can, I will be glad to have you make a thorough investigation of the circumstances of the case. * * * I consider it a matter of very great importance, and one that should occupy the careful attention of specialists. I requested specimens to be sent to Mr. Ryder for his examination, but an investigation in the field on the sick and dying fish will be of much more importance. Yours truly, SPENCER F. BAIRD. I arrived at Nadison August 16 at 2.30 p. m., with seine, dredge, microscope, and a suitable apparatus for studying the fresh fluids and tissues of the diseased fishes, and for the permanent preservation of material of all kinds likely to throw any light on the subject under investigation. Through the kind assistance of Eon. Philo Dunning, of Madison, president of the Wisconsin State Fish Oommission, a work-room was obtained at once in the boat-house of the steamer company, at the principal landing, and I spent two hours on the lake the same afternoon in search of dead and dying fish. I remained here until August 22, making collections as opportunity offered, carefully examining the freshest obtainable specimens for evidence of fungous parasit- ism, making numerous autopsios of fishes recently dead, preparing and staining slides of the blood and other fluids of those not yet dead when taken, for bacteriological atudy, and preserving the tissuea of such fishes for later histplogical work. I also dredged the lake along shore and in deep water, as described in a foregoing part of this paper, but lack of time prevented my making as extensive general collections as was to be desired. -~ * This fish was introduced from Lake Michigan some years before, according to information given me by Mr. Philo Dnuuing and others. INVERTEBRATES OF LAKES GENEVA AND MENDOTA. 483 During the first two or three days it was not difficult to find floating on the lake, among hundreds of putrescent bodies, now and then one which presented a fairly fresh appearance, the gills unaltered, the eyes not sunken, and the color bright. During many hours rowing, however, I saw but two perch in the act of dying and succeeded in capturing but one. The actions of these perch were precisely those described by previous observers as characteristic of .the death struggle of the diseased fish. They were at the surface, fluttering their fins, spinning irregularly about or scarcely moving at all, ofteu gasping as if for breath, rolliug over on their sides or backs between convulsions, and occasionally, for a few moments, disappearing' from sight or swim- ming feebls and irregularly along. The single sick fish captured, I took while it was still struggling, but i t scarcely moved after i t was landed in the boat. Slides of the blood of this fish, taken with a, pipette from t h e auricle of the lieart and from the venous sinus, were at once prepared, and its viscera were placed in 94 per cent. alco- hol within a half hour of its death. I: made similar preparations of the fluids and organs of other perch that had died OF the disease-the freshest I could obtain-and dissected twenty-four of them for a, study of the contents of their alimentary canals. I n preparing the blood, I used tho common method of making slides for bacteriolog- ical study, drying rapidly upon a cover glass a thin film of the blood, flaming it in the blaze of an alcohol lamp, staining with a glycerine solution of methyl violet or of Bismark brown, and mounting in Canada balsam. The general appearance of recently-dead specimens was that of' a heaIthy fish. They were, almost without exception, in good average condition, often fat and plump; a fact noticed with astonishment by all who gave the matter any close attention. The color was always bright, and the surface everywhere clean, and without a trace of fun- gous attack. The gills were very commonly congested, but not appreciably more so than those of a fish dying in the air. Their mucous membrane was seemingly always quite uninjured, and was certainly SO in several specimens of which I examined the filaments microscopically; and there was uo trace of parasitism, fungous or animal, in the gills of any fish I took. The heart was always distended with blood and some- times so gorged that the bulging of the venous sinus was visible from without. The liver was likewise congested, but seemingly by mechanical causes, as its tissues gave no evidence of infiltration. The blood itself was nor.ma1, the corpuscles in perfect con- dition, and both they and the plasma free of bacteria. The alimentary canal pre- sented no unusual appearance, and was commonly fairly well fllled with food, muoh of which had evidently been eaten rather recently. Many of the large Ohironomus larva, which composed the greater part of it in every case but one, were entire and still retained their dark red color. aoncerning the histological condition of the principal tissues of the diseased peroh I have unfortunately very little to ruport. My removal during the autumn of 1854from Normal to the University of Illinois a t Ohsmpaign, and the consequent transfer of the laboratory equipment and collections under my charge, made it impossible for me then to prepare and mount the material obtained for histological study, and this was kindly undertaken for me by a microscopist in Ohicago. From him 1 received later a good series of sections of liver, spleen, heart, brain, kidney, stomach, and in- testine of the lBBe herring, but a11 the material from the single perch taken alive ma8 destroyed by an unfortunate accident while in his possession, and I had left for study 484 BULLETIN OF THE UNITED STATES FISH COMMISSION. only some slides of the brain, heart, liver, and spleen, hurriedly prepared in the field from two perch which had been dead an unknown length of t i m e when taken. Apart from the gorging of the heart and congestion of the liver already mentioned and a noticeable amount of cellular degeneration in the liver and especially in the spleen, these slides gave no definite hint of the nature of the disease. This degenera- tion, very much more abundant in the herring, consisted of a conversion of the con- tents of the cells into a yellow, dark brown, or black mass of minute spherical gran- ules which had the appearance of micrococci ; but as they did not stain with aniliue they were very probably pigment granules instead; a supposition rendered more plaus- ible by the equal or greater pigmentation of the viscera which I have since noticed in many seemingly heal thy fishes. These altered cells were more abundant near the larger blood vessels, and where coueiderable numbers of them had undergone degen- eration their walls were often broken down, and the cells were thus replaced by a col- , lection of their dark yellow or black contents. From a general study of my fish collections and of the conditions prevailing in Lake Mendota a number of additional facts of some significance may be selected. (1) The herring, or so-called whitefish, of the lake were perishing in extraordi- nary number8 during the entire period of this outbreak, with symptoms precisely like those of the perch, and taking into account the relative numbers of these species in the lake, perhaps in as largeor eveu larger proportion. These herriug, like the perch, are, as is well known, bottom feeders, and in midsummer remain in the deeper waters. Furthermore, they die every summer, according to the uniform testimony of those with whom I talked, in precisely the same way a8 in 1884, but in very much smaller num- bers, The condition of the bodies of the fresh herring examined, two of which were taken before death, was precisely that of the diseased perch, except t'hat there was a greater amount of cellular degeneration of the viscera, particularly of spleen and kid- ney. Substantially all the substance of the former organ except the gorged blood vessels was replaced by masses of the spherical granules already described, or by cells filled with them, and the kidneys of the specimens examined were so loaded with them as to be black to the naked eye. There follows from the above a considerable probability that the perch were affected by the same caum a8 the herring, or else that the disease was a contagious cine and taken from the herring directly. It is further likely that this cause is present every year, as is shown by the regular death of a small number of the latter fish, but that its action was greatly intensified in 1884. (2) The majority of the perch dying were full grown, and absolutely no young were seen either by myself or by any one with whom I talked. The captain of the passenger steamer, who spends most of his time OD this lake, had seen none dead less than 6 or 6 inches iu length and of an estimated age of three or four years. The smallest specimens which I saw were at least half grown; but according to Professor Birge, of the University of Wisconsin, a few specimens were seen not over 3 or 4 inches long. (3) There was a marked contrast in food between the dead and diseased fishes and the healthy ones taken by the use of the seine in the shallow waters along shore. The former had eaten, almost WithOlJt exception, little or nothing but a large red Chi- rouomus larva living, as shown by the notes 06 collections given in the preceding part of this paper, in the mud of the deeper water, while the healthy fishes taken in the seine had not fed at all upon these large red larvae, but ouly upon smaller white INVERTEBRATES OF LAKES GENEVA AND MENDOTA. 485 larva of another species of Ohironomus and upon a variety of the smaller animal forms occurring among the weeds in the shallow water. The following are the details of the food of fourteen diseased perch and of nine healthg ones taken by hook or seine at the aame time, the numbers being those from m y laboratory catalogue of accessious. BOOD OF DISEASED PERCH. 4929. The intestine of this specimen was empty, but the stomach was well filled 4947. Pull of large red Chironomus larva" 20 to 25 millimeters in leugth, and 4948. A greet quantity of food, consisting of the usual large red larvae and pupae 4949, A moderate amount of the large Chironomus larvae and p u p a 4960. A rather small quantity of larva aud pupa of red Chironomus, with some 4951. A moderate amount of the same material. 4932. Red Uhirouolnns larva aud pupa, as usual, in very large quantity. 4953. The usual larva and pupa of Ohironomns only. 4954. As above, the larva 'LO millimeters in length. 4955. A great quantity of food of the usual cliaracter and uothing else, the pupa 4956 and 4957. Larvm and pupa of the red Chironomus only. 4958, This specimen furnished the only exception to the usual food of the dead Iwch taken. The stomach oontained a moderate number of nymphs of Ephemera and ;I, few small white l a r v a aud pupm of Ohironomus, the larvae 10 inillimeters long. Ala tl~ough dead when taken, i t is possible that this fish had not perished by disease. The objects which i t had eaten are those found in relatively shallow water. 4961. A rather Stndl amount of food, not recently taken, the pupa and larva of the red Chironomus being chiefly in fragments. he contents of the alimentary canal of ten other specimens, not examined microscopically, was evidently of the same character. with larvae end pupae of the large red Chironomus. pupa of the same species 16 inillimeters long. of Ohironomus, 15 millimeters long, with some very fine dirt. very fine dirt. A single crushed entomostracan of the order Cladocera. predominating. BOOD OF HEALTIIY PERCH. 4945. chiefly larvae and pupa of Ohironomus, the former white, 10 millimeters long; also two or thrde specimeiis of Allorclbestes deibtata, and a long and slender case- worm with tube of sand. 4946. A consider&blt? uumbur Of small h v a ? a i d pupa of Chironomus, white in color, several Allorckestes dentata, a single casewortn with sand tube, one specimen of Eurycercus lamellatus, and a single CYC~OPS. food of these Inrv:u, deteriuined by disseotiou, oousisted of very fine mud, with IL great quantity of minute vegeteble dhbris, oo~upos~d of vnrious kinds of oellulnr structures. These were evi- dently in estate of decomposition, as Shown by the Vast uumbers of bimilli aut1 Other bnoteria everywhere a~nong the oontents. There was also oocasional~y D filementous alga redembling Osoillarin, and a few unioellular nlgm were noted. . -___ * 48 6 BULLETIN OF THE UNITED STATES FISH COMMISSION. 4959. Chiefly the small white Chironomus larva, and pupa of the same, several examples of Allorchestes, a few nymphs of the genus Ephemera, a single Burycereus lamellatuk, and fragments of filamentous Alga, with some other vegetable particles. 4960. A considerable quantity of the larvae and pupae of Chironomus already mentioned, -the former 9 to 10 millimeters long,-together with immature Ephemera and fragments of filaqentous Alga. 4962. This specimen added to the usual Chironomus larva and pupae which formed the greater part of the food, a few Allorc?bestes, a young larva of Ephemera, a Corixa larva, a small leech, and a single young Sphaeriiim. 4963. Many specimens of Allorchestes dentata, a few caseworms with their sand- tubes, several nymphs of Ephemera, a considerable number of small chironomid larvae, and two specimens of Cyclops. 4964. Chiefly larvae aud pupa of the small Ohironomus. Besides these a few caseworms and specimeus of Allorchestes. 4965. (Prom Third Lake.) Several of the usual small Chironomus larva, a larva of Corethra, and the mollusk Physa. 4985. The stomach of this example contaiued only la rva and pupa of the small Ohironomus. I n the intestine,' besides the above, there were two caseworms in their cases. (4) All the facts just cited tend to show that the perch perishing were ranging in the deeper water, and that they had almost invariably made their last meal of insect larva found only in the mud of the deeper parts of the lake; that they had been, in short, in company with the herring likewise notably diseased. I was informed by a fisherman familiar with the lake and its inhabitants that i t was an extraordinary thing to find the perch ranginginto deep water in midsummer, although they were frequently found in numbers iu the depths of the lake in wiuter, when fished for through theice. I n these wiuter specimens red '' worms" (Chironotnus larva 9 ) were often noticed. (5) The mud from the deeper part of the lake, as has been already mentioned, had a peculiar rank and almost stinking odor, and contained a considerable quantity of organic matter undergoing mor8 or less rapid decay. (6) Acomparison of my collections from Lake Mendota with those from Lake Geneva, reported in this article, and especially with my much more abundant collec- tions made from the lakes in northern Illinois, shows an unusually small proportion of may-fishes, Aselli, Allorchestes, and other crustaceans ordinarily common in our lakes among the weeds and shallower waters generally, and a correspondingly large percent- age of Chironomus larva in the food of all the perch examined,-a fact which hints at the probable deficiency in this lake of the kinds of insect larvae and crustaceans usually selected by the perch. (7) The weather of the summer had been warm and rather showery, but not in any way especially remarkable. There was, however, one heavy flooding rain not long be- fore the outbreak of the fish disease, which may well have washed into the lake unusual quantities of organic matter from the swamp beyond Catfish Bay and 'from the sur- rounding country. Any organic accumulations due to such an occurrence would neces- sarily have been more evident in Lake Mendota, the uppermost of the ohain, and that with the largest drainage basin, than in any of the lakes below. (8) What seem, from the best information I can obtain,quite similar cases of destruction of our native fishes, are of rather common occurrence in t h e rivers of Illi- INVERTEBRATES OF LAKES GENEVA AND MENDOTA. 487 nois in the hottest weather of the year. They usually, if not always, follow upon flooding rains, and thus occur when the streams are full or overflowing with turbid water loaded with the products of decay. They are sometimes succeeded by g ra t deposits of rotting fish along the river front of towns, .requiring burial to protect the general health. We have in the facts reported here abundant material for surmise and the con- struction of hypotheses ; but no means. of precise verification. Arriving at Lake Men- dots after the practical cessation of the epidemic argued tt disappearance or a great reduction of its cause, and unable to obtain good material enough from which to gen- eralize, I have withheld this report iu the hope that a Aimilar occurrence within my reach might enable me to complete the investigation. Several of the kind have, in fact, been noticed in Illinois within recent years, knowledge of which has reached me through our State Fish Commission, but always much too late to permit successful study. It thorefore now seems to me best merely to put on record the facts already ascertained, and to postpone discussion until more evidence has been collected.