442 



COLLEGE ZOOLOGY 



come free from the yolk, and the young fish breaks out of the 

 egg membranes (7) . The young fish lives at first upon the yolk 



in the yolk-sac (7, y.s), 

 but is soon able to 

 obtain food from the 

 water. This consists 

 of small crustaceans ; 

 insects are added after 

 a time, and still later 

 larger crustaceans, 

 mollusks, and small 

 fishes. 



Economic Impor- 

 tance. The perch is 

 perhaps the best pan- 

 fish among American 

 fresh-water fishes. In 

 many localities it is 

 taken largely for mar- 

 ket. It is not a good 

 game-fish, but has one 

 advantage it is easy 

 to catch. The perch 

 has been introduced 

 successfully into sev- 

 eral small lakes in 

 Washington, Oregon, 

 and California. It can 

 be artificially propa- 

 gated, but other fishes, 

 such as whitefish, lake 

 trout, and pike-perch 

 are of commercial im- 

 portance and are, therefore, preferred for propagative purposes 

 to the yellow perch. 



FIG. 374. Nine stages in the development 

 of a fish (Salmo fario). A-H, before hatching; 

 I, shortly after hatching. bl, blastoderm; 

 emb, embryo; r, thickened edge of blastoderm; 

 y.s, yolk-sac. (From Parker and Haswell ; 

 A-G, after Henneguy.) 



