BULLETIN OF THE UNITED STATES FISH COMMISSION. 249 



tine is often not yet very densely packed with food even at this 

 period. At the age of three weeks an abundance of food is found 

 in the intestine, that portion which becomes the stomach and which 

 extends from the posterior extremity of the liver to near the vent 

 being greatly distended with aliment. Upon investigating the nature 

 of this food material we learn that it consists almost entirely of very 

 small crustaceans, in reality for the most part of the very youngest 

 Bcqjhniadw and Lynceiflcv; only once did I find what I thought might 

 be very small OstraGoda or Cypridw. In some instances the undevel- 

 oped larvai of Daphniw were noticed. In a few cases green cellules 

 were observed in the intestines of shad larvse resembling Protococcus, 

 but as this material appeared to be accidental, it is probably not an im- 

 portant element of shad food. In the young fishes the dark, indigesti- 

 ble remains of the food of the Daplinice always remained, together with 

 the hard chitinous parts, as long-curved cylindrical casts which pre- 

 served the shape of the intestines of the crustaceans. In one young 

 shad, twenty-two days old from the time of impregnation, measuring 

 14 millimeters in length, I estimated from a series of sections through 

 the specimen that it must have consumed over a hundred minute crus- 

 taceans. 



The oldest specimens of artificially reared shad which came into my 

 hands were some that had been overlooked in some of the hatching 

 apparatus at Dr. Gapehart's fishery in North Carolina, where they re- 

 mained for three weeks after hatching. In that time they had grown 

 to a length of 23 millimeters, or almost one inch. The air-bladder was 

 more developed and the stomach was more decidedly differentiated 

 than in any previous stage. In the intestines of these I found, beside 

 black, earthy, and vegetable indigestible matter, the remains of the chit- 

 inous coverings of small larv^al Diptera, and the remains of a very 

 small adult crane-fly, besides Entomostraca allied to Lyneeus. In these 

 specimens the dorsal fin had the rays developed, the continuous median 

 larval natatory folds having by this time disappeared. 



The mode in which the young fish capture their Entomostracan prey 

 may be guessed from their oral armature. Most fish larvos appear to be 

 provided with small, conical, somewhat backwardly recurved, teeth on 

 the jaws. Rathke, in 1833, described the peculiar hooked teeth on the 

 lower jaw of the larvEe of the viviparous blenny, and Forbes has ob- 

 served minute teeth on the lower jaw of the young Coregonus albus. I 

 have also met with similar teeth on the lower jaw of the larval Span- 

 ish mackerel. 



THE FOOD OF THE ADULT SHAD. 



The mouth of the adult shad, as is well known, is practically tooth- 

 less, and in the throat there are no functionally active teeth, as in the 

 larvai, so that the latter, in reality, have a relatively much better de- 

 veloped dentary system than their parents. The adult, moreover, prob- 



