130 



than anything else. It should be noted, however, that nearly half 

 the specimens were derived from places where Entomostraca were 

 excessively abundant at the lime of their capture. 



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 diminished 

 length of the alimentary canal. We have now also a decided pre- 

 dominance of animal food, which is about three fourths of the entire 

 amount, and nore 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 larvtf 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 character, only about a third of it 

 being derived from aquatic plants. 



GrROUP IV. 



Intestine sliort ; teeth hooked, without fcfiuding sui-face. 



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 Illmois. It was not thought 

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

 to live of them ; namely, to Minnilus, Photogenis, Phenacobins, 

 Semotilus, and Ceratichthys. 



Minnilus atheeinoides, Raf. Emerald Minnow. 



This species is everywhere abundant in streams and lakes, but 

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

 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 Alga?. A minute fish 

 had been eaten by one of these minnows. Insects made two thirds 

 of the food, nearly two thirds of them being terrestrial. Neurop- 

 terous larvffi were the principal aquatic forms, clnetly ease-worms 

 and larvffi of ephemerids. The Crustacea (twenty-two per-cent. i 

 were all Entomostraca, about two thirds of them Cladocera, the re- 

 mainder Cope pod a. Among the former Bosmina and .Chydorus were 

 recognized, and Diaptomus among the latter. 



