74 The Food of Young Fishes. 



Olupeid^. 



We come next to twelve specimens of the gizzard-shad 

 (Dorysoma), whose minute fry swarm in countless num- 

 bers in the waters of our larger rivers in midsummer. These 

 were taken in June and July, from the Illinois R., from 

 Ottawa to Peoria. The smallest of the group were twenty 

 mm. long by two mm. wide, — as slender as cyprinoids and 

 nearly cylindrical, although the adult is a high, thin fish. 

 I was greatly interested by the discovery that the maxil- 

 laries of these smallest specimens are provided with teeth, 

 — a single row of nine or ten on the lower edge, — although 

 the mouth of the adult is entirely toothless and smooth. 

 The internal structure also differs remarkably from that 

 of the adult, especially in the much greater simplicity of 

 the digestive apparatus. In a young gizzard-shad seven- 

 tenths of an inch long by one-tenth high, the intestine was 

 found to pass from the anterior end of the stomach to the 

 vent with only one short forward turn of about a fourth the 

 length of the body cavity, made a little way behind the stom- 

 ach. Although the mucous surface of the intestine was at 

 this time very rugose, showing a commencing complication 

 of the digestive system, there was no trace of pyloric coeca. 

 The intestine was filled with Cypris, Chydorus, Alona, 

 Cyclops, etc. 



On the other hand, in a fish three and three-fourths inch- 

 es long, showing the general characters of the adult, the 

 intestine passed upward and backward from its origin, 

 running without flexure the whole length of the body cav- 

 ity (this part being covered with an immense number of 

 pyloric coeca), then turned forward to the stomach, ran 

 back from there about one-third of the way to the vent, 

 then turned forward and ran a tortuous course beneath the 

 stomach to the pericardial membrane and back again, also 

 tortuously, two-thirds of the way to the vent. From this 

 point it ran forward again to the stomach, and crossing to 

 the left side, ran repeatedly backward and forward in the 

 posterior part of the body cavity, making seven turns be- 

 tween the stomach and vent before opening, thus extend- 

 ing, in all, about eight times the length of the perivisceral 



