78 The Food of Young Fishes. 



Staurastruin and various diatoms among the Alga?, were 

 the principal genera. A minute Agrion larva, a very 

 young Amphipod, and larval Oopepoda (nauplius), were 

 the only other kinds recognized. It was obviously impos- 

 sible to make any estimate of the ratios of such minute 

 and varied objects occurring in such great quantity, and I 

 have contented myself with a simple enumeration. 



A specimen three inches long, from Peoria Lake, in Oc- 

 tober, had eaten only Oopepoda (Oanthocamptus) with a 

 trace of Ohironomus larvae. 



Ten specimens of red-horse (Myxostoma), varying in 

 length from an inch to two and three-fourths, taken in Ju- 

 ly and August, from the Fox and Illinois rivers and from 

 Mackinaw Or., show no important differences of food. 



In the smaller specimens, taken from the Fox and Illi- 

 nois, Entomostraca, especially Oyprids,were relatively more 

 important, sometimes constituting nearly the whole food ; 

 but no attempt was made to tix precise ratios. In the 

 four larger specimens from Woodford Oo., tests of Difflu- 

 gia were estimated to form eighty-five per cent, of the 

 contents of the intestines. These specimens were taken 

 one at a time, several miles apart, along a rocky part of 

 the stream. Besides the species of Difflugia and Arcella 

 given in the foot-note, various desmids and diatoms were 

 abundant, with filamentous Algae, rotifers (Squamella and 

 Rotifer vulgaris)., Oyclops, Alona, Pleuroxus and water 

 mites, Ohironomus and other Diptera larvae, some inde- 

 terminable vegetable matter and a single Thrips (Hemip- 

 tera). The small percentage of Ohironomus larva? shows 

 that this species has not the habit of the stone-roller. 



Two specimens of the common sucker {Catostomus com- 

 mersoiiii), six inches and six and three-fourths in length, 

 taken from Mackinaw Or., in August and June, had 

 eaten food so similar to that of the preceding genus that 

 detailed description is unnecessary. 



Two specimens of the commonest luff alo- fish (Ichthyo- 

 bus), seven-eighths of an inch long, had eaten most freely 

 of unicellular Algae (sixty-three percent.), of which only 

 Protococcus and Olosterium were recognized. Specimens 

 of Anuraea were reckoned at twenty-seven per cent., and 



