58 CLARENCE L. TURNER Vol. XXII, No. 2 



To the first group belong Percina caprodes and Boleichthys 

 fusiformis. To the second belong Cottogaster copelandi and 

 Boleosoma tiigrum, while Etheostoma variatum, E. ccBruleum and 

 E. flabeUare comprise the third. Diplesion blen?iioides, Hadrop- 

 terus aspro and H. phoxocephalus are related to both groups one 

 and three and Animocrypta pellticida resembles group three. 



FACTORS GOVERNING FOOD CHANGES. 



{a) Age and Size of Fish. 



It is obvious that the smaller fish must be limited in their 

 selection of food to such a size as it is physically possible for 

 them to capture, while the larger ones have a greater possibility 

 of choice. Since the size of the fish is dependent on its age, the 

 age must enter into this principle. Records were kept of the 

 size of the food animals taken by Percina caprodes, Etheostoma 

 cceruleum, E. flabeUare and Boleichthys fusiformis and this 

 record compared with that of the length of the fish. A close 

 degree of similarity was found between the size of the food 

 animals and the size of the fish, which was quite independent 

 of the character of the food. 



(b) Seasonal Position of Food Animals. 



Whether the body of water in question is a stream, a small 

 lake or a large lake such as Lake Erie, there is a season cycle 

 in the fauna and the flora. Phyto-plankton develops which 

 furnishes the food for the minute crustaceans and their larvae 

 and for the larval forms of some insects. Submerged and float- 

 ing vegetation develops which furnishes food and a retreat for 

 insects, crustaceans and young fish all of which are important in 

 the food relations of the darters. With the warming of the 

 waters winter eggs of various forms hatch and the young forms 

 produced are also important as food animals. Even eggs of 

 insects and of fishes furnish food at certain seasons. Like all 

 other fishes the darters are dependent for the amount and vari- 

 ety of their food upon the seasons in which they develop. 



(c) Special Structures. 



Forbes has pointed out that those fishes that retain the 

 habit of feeding upon minute organism in their adult stages are 



