BULLETIN OF THE UNITED STATES FISH COMMISSION. 245 



the forests of fixed protozoa, just as Planorbis, Lymnaeus, and Physa 

 pasture upon the protozoa, algse, diatoms, and desmids, in fresh water. 

 The great abundance of Copcpoda and Amphipoda is, however, the best 

 evidence of the abundance of still smaller forms adapted to furnish 

 them with food. What multitudes of forms besides Copepoda must 

 largely subsist upon the protozoa and protophytes. Of such groups 

 we may name the Lamellibranchs, Pteropods, Worms, Bryozoa, Porifera, 

 and, doubtless, many Coelenterata. Some of these, notably the Lamel- 

 libranchs, could probably not exist were it not for the numerous proto- 

 zoa and j)rotophytes, upon which, from necessity, they are comiielled to 

 feed. 



What is true of the fauna of the sea appears to be in an equally great 

 measure true of the faunae of fresh-water ponds, lakes, and streams. 

 Eecently I investigated some Daplmiadce which had been kept for some 

 time in an aquarium; to my surprise I did not find any recognizable re- 

 mains of animal food in the intestine. The latter were, however, entirely 

 filled with a sarcode-like material, doubtless in jiart a digestive secre- 

 tion, together with, what might have in ijart been animal food. The 

 vegetable food, consisting of diatoms, unicellular algte, spores of fungi, 

 fragments of oscillatorise, were so sparingly mixed with the intestinal 

 contents that they could not be regarded as contributing much to the 

 nutrition of the animal. The black or brown material, sometimes filling 

 the intestine of Entomostraca, I find to consist in great part of humus, 

 particles of quartz sand and earthy matters, which are of course indi- 

 gestible, being thrown out of the vent, as in Chirocephali, in the form 

 of cylindrical casts. 



The most valuable contribution to our knowledge of the food of the 

 fresh-water fishes of the western United States has been made by Pro- 

 fessor S. A. Forbes, in Bulletins Xos. 2 and 3 of the Illinois State Labora- 

 tory of ISTatural History, for the years 1878 and 1880. With the most 

 painstaking care the results of a vast number of examinations are re- 

 corded. He finds that the Darters, Perches, Lahracidce, Centrarchoids 

 or sun-fishes, Scisenoids, Pike, Bony Gars, Olupeoids, C^'prinoids, Suck- 

 ers, Cat-fishes, and Amia, both the young and adults, consume large 

 numbers of small aquatic, and occasionallj'' small terrestrial organisms, 

 notably the smaller Arthropods. While many of the more voracious 

 species, both young and adult, feed on their immediate allies, the dietary 

 of the fishes of Illinois, according to this observer, includes mollusks, 

 worms, fresh-water Polyzoa, Hydrachnidse, insects of both mature and 

 larval forms; Crustacea, embracing Decapods, Tetradecapods, Amphi- 

 pods, Isopods, and Entomostraca of the groups Cladocera, Copepoda, 

 and Ostracoda; Eotifera, Protozoa, vegetable matter, and algse. In his 

 first paper he also gives a hst of the organisms found in the stomachs 

 and intestines of the Pirate perches, Gasterosteidci', Atherinidm^ Cyprin- 

 odontidce, Umbridce, Hyodontidcv, and Folyodontidce. Both are accom- 

 panied by elaborate comparative tables, and, in an economical sense, 



