86 The Food of the Smaller Fresh - Water Fishes. 



Summary of the Group. 



Taking now this group as a whole, we remark, first, the absence 

 of mud mingled with their food, as related to the greatly dimin- 

 ished length of the alimentary canal. We have now also a 

 decided predominance of animal food, which is about three-fourths 

 of the entire amount, and note likewise the first occurrence of 

 fishes. Although Mollusca occur in this group, it is in quantity 

 too small to appear in the ratios. Insects make about half the 

 food of all, nine per cent, being terrestrial forms. The larvas of 

 Neuroptera are by far the most important insect species, and 

 stand at twenty-five per cent. Entomostraca make a fifth of the 

 whole food, distributed among all the orders. The vegetation 

 eaten was largely of a purely miscellaneous and incidental char- 

 acter, only about a third of it being derived from aquatic plants. 



Group IV. 



Intestine short; teeth hooked, without grinding surface. 



This group, organized more strictly for predatory purposes than 

 any of the preceding, contains also the largest number of genera, 

 embracing nine of those occurring in Illinois. It was not thought 

 necessary to study all of these, and my dissections were confined 

 to five of them, namely: to Minnilus, Photogenis, Phenacobius, 

 Semotilus and Ceratichthys. 



Minnilus atherinoides, Raf. Emerald Minnow. 



This species is everywhere abundant in streams and lakes, but 

 does not occur in ponds. It is most common northward, swarm- 

 ing in summer along the shores of Lake Michigan. 



The gill-rakers are short, triangular, and about one-fourth the 

 length of the filaments; and the intestine is less than the length 

 of the head and body. 



Eighteen specimens were studied, all from the northern half of 

 the State. The food was almost strictly animal, but five per cent, 

 consisting of vegetation, and this chiefly of accidental character, 

 occurring in trivial ratios. Only a single specimen had taken 

 about forty per cent, of its food from filamentous Algae. A 

 minute fish had been, eaten by one of these minnows. Insects 



