Page:First course in biology (IA firstcourseinbio00bailrich).pdf/356

 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 neighborhood; in the markets of your town.

The egg-cells and sperm-cells are pressed out into a pan of water.

, with yolk-sac adhering, eyes large, and fins mere folds of the skin. (Enlarged.)

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 intelligence, 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