66 
The Food of Fishes. 
in the stomachs of Centrarchus, is accounted for by the 
fact that the youngest specimens of this genus were 
taken from small mud-holes, favorable to the occurrence 
of Entomostraca of that order. The uniformity of food 
at this time implies that the selective apparatus of these 
fishes, whatever its construction, has not yet grown be- 
yond the size of these minute animal forms. 
From the second table of one hundred and six speci- 
mens we learn that with a general change of food from 
Entomostraca and Chironomus to larger Crustacea and 
insects, there appear certain differences — notably the 
continuance of Entomostraca as the most important ele- 
ment in Pomoxys, and the occurrence of mollusks in Eu- 
pomotis and of fishes in Micropterus. It is important to 
recall, at this point, that Pomoxys has the largest, finest 
and most numerous gill-rakers of the group — the best 
straining apparatus, in short — that Eupomotis has stout, 
blunt pharyngeal teeth, and that the black bass have 
relatively the widest mouths of all. It is also to be noted 
that the large-mouthed-bass commenced to take fish when 
an inch and a quarter long, and the small-mouthed spe- 
cies not until it reached a length of two and a half inches. 
It will also be observed that Entomostraca are least 
abundant in the food of the small-mouthed black bass and 
the rock bass— species found usually in swift and shallow 
water, when of this size. The importance of water-bugs 
(Corixa) to the first three species of this table is evident. 
From the table of adult food we find that these com- 
mencing peculiarities of the preceding table become here 
more prominent. All the Entomostraca of this table, ex- 
cept insignificant traces, now appear in the food of Po- 
moxys ; the molluscan food of Eupomotis is nearly five 
times that of any other genus ; and the ratios of fish food, 
running from eighty-six j)er cent, down to nothing, when 
arranged in a series, are seen to correspond, with curious 
exactness, to a series of the species themselves arranged 
according to the relative sizes of their mouths. 
I was disappointed in being unable to find any food 
characteristics corresponding to such minor differences 
in the length of the gill-rakers of the anterior arch as ap- 
