312 GENERAL ZOOLOGY 



spawning varies with the climate ; in the South it begins as 

 early as March ; in New England, in May. The eggs are laid 

 in shallow water in a ribbon-like mass, which, after absorption 

 of water, is sometimes six or seven feet long and two inches 

 in diameter. This great mass, which contains thousands of 

 eggs (over a hundred thousand have been counted irr a two- 

 pound perch), is fertilized by the male emitting his sperm 

 (milt) over it. The eggs form a large part of the food of 

 other fishes and aquatic birds, and were it not for their great 

 numbers few would ever hatch. In from two to four weeks, 

 depending on the temperature, the young perch hatches from 

 the egg, at first with the yolk-sac attached to the ventral sur- 

 face (compare Fig. 155). After absorption of the yolk-sac, 



which soon occurs, the young 

 perch differs from the adult 

 chiefly in its smaller size and 

 lighter color, and in the rela- 

 tively greater size of head 

 FIG. 155. Young Sturgeon with Yolk- -, n .^ ,, 



Sac. Enlarged. (After Ryder) and e y es as compared With the 



rest of the body. 



Relation to Environment. The whole organization of the 

 perch marks it at once as one of the predatory type of ani- 

 mals, those which hunt their food and depend upon their 

 superior strength or agility to obtain it. As Izaak Walton 

 long ago said of its European relative, the yellow perch is 

 " one of the fishes of prey that, like the Pike and Trout, car- 

 ries his teeth in his mouth, not in his throat, and dare venture 

 to kill and devour another fish." The shape of the body is pre- 

 cisely that which offers least resistance to motion in the water. 

 The strong lateral muscles afford an economical method of 

 applying power for propulsion to the caudal fin, which, by a 

 slight lateral motion, drives the fish forcibly forward. Lateral 

 and median fins assist in maintaining equilibrium, in steering, 

 and in raising and lowering the fish in the water. 



