160 AMERICAN FISH CTJLTUEE. 



"The specific gravity of the eggs at all stages is very 

 small — harely enough to sink them in still water — a great 

 contrast to those of the trout, which go down almost like 

 shot. 



" The newly-hatched young is ^^^ of an inch long. It 

 swims actively by a continuous and rapid vibration of the 

 body, and keeps its head to the current, perhaps to get the 

 food that is carried past.* The yolk-sac, whose longer 

 diameter, already in the egg, was parallel with the body, 

 now appears still more ovoid in form. The pectoral fin is 

 easily seen, and the finger-like canals in it indicate that its 

 rays are forming. The embryonic, dorsal, caudal, and ven- 

 tral fins are continuous one with another, and extend round 

 the whole body, back of the yolk-sac. In the caudal a 

 few faint, radiating fibres indicate the formation of rays. 

 The choroid has completed its circle, and the eye has 

 nearly the outward look of that in the adult. Along the 

 course of the alimentary canal, quite to the anal opening, 

 and over the yolk-sac, the pigment stars are more numerous 

 and defined. A little indentation indicates the mouth, 

 which lies under the eye, and opens as a curved slit. The 

 general mass of the brain is easily made out. Along the 

 centre of the body, a more translucent stripe indicates the 

 dorsal cord, above which the range of muscular bundles 

 begins to be distinct. 



* The current carries the fry gradually seaward. Hence it is, 

 that since the erection of the Holyoke dam, young shad are no 

 more seen there ; because, by the time they are large enough to be 

 noticed, they have all drifted lower down the river. 



