120 



ANIMAL BIOLOGY 



FIG. 226. ARTIFICIAL FECUNDATION. The 

 egg-cells and sperm-cells are pressed out into 

 a pan of water. 



paddle for sculling? 

 An oar? State several 

 reasons why the head 

 of the fish must be 

 very large, although 

 the brain is very small. 

 Does all the blood go 

 to the gills just after 

 leaving the heart ? 



Make a list of the 

 different species of 

 fish found in the 

 waters of your neigh- 

 borhood ; in the markets of your town. 



4 ^^Reproduction. The female fish deposits the unfertilized 

 eggs, or ova, in a secluded spot on the bottom. Afterward 

 the male fish deposits the sperms in the same place (see 

 Fig. 225). The eggs, thus unprotected, and newly hatched 

 fish as well, are used for food by fish of the same and other 

 species. To compensate for this great destruction, most 

 fish lay (spawn) many thousands of eggs, very few of 

 which reach maturity. Higher vertebrates (e.g. birds) have, 

 by their superior in- 

 telligence, risen above 

 this wasteful method 

 of reproduction. Some 

 kinds of marine fish, 

 notably cod, herring, 

 and salmon, go many 

 miles up fresh rivers 

 to spawn. It is possible that this is because they were 

 originally fresh-water species ; yet they die if placed in 

 fresh water except during the spawning season. They go 



FIG. 227. NEWLY HATCHED TROUT, with 

 yolk-sac adhering, eyes large, and fins mere 

 folds of the skin. (Enlarged.) 



