47 



its larger tributaries. It is a large species, reaching a weight of 

 thirty pounds and upwards and a length of six feet or more, 

 including the paddle-like snout. Although ?o large, the greater 

 part of its food consists of the smallest aquatic Crustacea and 

 insect larvae, strained from the water by means of an extraordi- 

 nary apparatus in the gills, composed of long and slender gill- 

 rakers, a double series on each arch, and over five hundred in a 

 series. Interlocking as these do when the gill apparatus 

 is extended, they form a strainer sufficient to arrest the smallest 

 living forms above the Protozoa, and with the immense opening 

 of the mouth and equally free provision for the exit of water 

 from the gill chamber, enable this fish to strain out enormous 

 quantities of these minute animal forms, especially those most 

 commonly reserved for young fishes. It takes also, in mid- 

 summer, insect larvae of medium size, but evidently avoids 

 vegetation, and never swallows mud. 



FOOD OF THE YOUNG. 



By an examination of three hundred and one specimens, 

 representing twenty-seven species, twenty-six genera, and twelve 

 families of Illinois fishes, I learn that the food of many species 

 of fishes differs greatly according to age; and that, in fact, the life 

 of most of our fishes divides into at least two periods, and that 

 of many into three, with respect to the kinds of food chiefly 

 taken. Further, in the first of these periods a remarkable simi- 

 larity of food was noticed among species whose later feeding 

 habits are widely different. The full-grown black bass, for ex- 

 ample, feeds principally on fishes and crayfishes, the sheeps- 

 head on moUusks, and the gizzard shad on mud and Algae, while 

 the catfishes are nearly omnivorous ; yet all these agree so 

 closely in food when very small, that one could not possibly 

 tell from the contents of the stomachs which group he was 

 dealing with. 



In the earliest stage, all the fishes studied, except suckers 

 and minnows, depend for food on the smallest crustaceans, 

 commonly called Entomostraca, and on certain small worm- 

 like larvae of gnats or gnat-like flies scarcely larger than these 

 crustaceans, and usually occurring with them. By far the most 



