76 
On the Food of Young Fishes. 
of considerable size — six inches long or more — upon 
food more trivial than Copepoda or Lynceidae; viz., upon 
rotifers, Protozoa and unicellular Algae. While only such 
Protozoa were found as are furnished with firm tests or 
carapaces, yet the abundance of Difflugia and Arcella in 
the intestines of these fishes leaves little doubt that the 
more perishable Protozoa must also be taken in consider- 
able quantity. It is an interesting fact that even here the 
smallest specimens were found feeding on Entomostraca 
only, and it is therefore possible that these form the first 
food of the family. 
Ten specimens of the stone-roller ( Hypentelium nigri- 
cans ), ranging from one and three-eighths to three inches 
represent two dates and localities. The four smallest, 
none larger than an inch and tliree-fourtlis, were taken 
from the lower Fox, July 9, 1879. The others were ob- 
tained from Mackinaw Cr., in Woodford Co., 111., in the 
latter part of August. The situations were similar, both 
streams being swift and rocky where these fishes were 
caught. Their food was chiefly the larvae of Chironomus 
(ninety per cent.), the remaining tenth being principally 
made up of Alona (six per cent.). Ostracoda, Copepoda, 
and Algae each made about one per cent, of the food. The 
Algae were mostly diatoms and desmids, Closterium being 
especially common. Many Difflugia and Arcella were 
also found in these fishes. 
We trace in this a remarkable resemblance to the food 
of the darters, which, it will be remembered, frequent 
similar situations. Lacking the sucking mouth of Hypen- 
telium, they do not take Protozoa or unicellular Algae, 
but in other particulars agree closely with this species. 
This curious fish is peculiar among the suckers in the un- 
usual development of the pectoral fins — a distinguishing 
feature of the darters likewise — doubtless related, in 
both cases, to the constant struggle with a swift current. 
We may also remark the darter-like glow of color in the 
young of this species — a very peculiar distinction among 
the Catostomidan. This is one among many facts which 
indicate that exposure to light has great primary effect 
on the color of fishes — an effect often suppressed. 
