92 
The Food of the Smaller Fresh - Water Fishes. 
these facts we find upon analysis to be evidently due to Phenaco- 
bius, by which genus nearly all the Chironomus larvae were taken; 
and this, as already shown, is explained not by any structural 
feature, but by its peculiar habitat; and when we note that 
aquatic larvae together amount in Group III to twenty-five per 
cent., and in Group IV to twenty-seven, we see that the signifi- 
cance of the difference mentioned disappears. A similar explana- 
tion is found of the difference in the ratios of Entomostraca, — 
that of the first group amounting to twenty per cent, and that of 
the second only to four. An examination of the tables shows that 
this predominance in the group first mentioned is nearly all tracea- 
ble to Hemitremia, a very small fish with rather elongate gill-rakers. 
The importance of these gill structures is still more clearly 
indicated, as already noticed, by the difference between Notemi- 
gonus and Chrosomus of the second group, and clearly far out- 
weighs the structure of the teeth |fis an indication of the food 
habits of the fish. 
The general conclusions reached may be thus briefly stated :» 
An extraordinarily elongate intestine indicates the limophagous 
habit, rather than an especial preference for vegetable food. The 
length or number of the gill-rakers has much to do with the 
abundance of Entomostraca and other minute animal forms in the 
food of the fish, while the presence or absence of the terminal 
hook or the masticatory surface to the pharyngeal teeth is not thus 
far shown to have any sensible influence upon th£ general average 
of the food. Finally, a species may depart widely in food char- 
acters from those more nearly allied to it in structure, if its 
favorite haunts are peculiar. 
