76 The Food of Young Fishes. 



ers of considerable size — six inches long or more — upon 

 food more trivial than Oopepoda or Lynceidte; viz., upon 

 rotifers, Protozoa and unicellular Algas. While only such 

 Protozoa were found as are furnished with firm tests or 

 carapaces, yet the abundance of Difilugia and Arcella in 

 the intestines of these fishes leaves little doubt that the 

 more perishable Protozoa must also be taken in considera- 

 ble 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 {Hyjpenteliutn 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 three-fourths, were taken 

 from the lower Fox, July 9, 1879. The others were obtained 

 from Mackinaw Or., 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 larvre of Ohironomus (ninety 

 per cent.), the remaining tenth being principally made 

 up of Alona (six percent.). Ostracoda, Oopepoda, and 

 Algee each made about one per cent, of the food. The 

 Algge were mostly diatoms and desmids, Olosterium 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 simi- 

 lar situations. Lacking the sucking mouth of Hypenteli- 

 um, they do not take Protozoa or unicellular Algge, but in 

 other particulars agree closely with this species. This cu- 

 rious fish is peculiar among the suckers in the unusual de- 

 velopment 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 Oatos- 

 tomidas. 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, through natural se- 



