THE JOINTED-FOOT ANIMALS 



141 



replaced by true tissue. This periodic growth of the lobster 



really begins before the act of molting takes place; in fact, 



the physiological need for more room is what brings about the 



act of getting rid of the old exoskeleton. The number of 



molts an individual lobster may have depends, in a great 



measure, upon the abundance of its food. Males molt more 



frequently than females ; hence the largest lobsters are always 



males. Very young lobsters molt more 



frequently than those of the size we 



find in the market. During the process 



of molting it sometimes happens that 



an appendage is broken off. In the 



ordinary course of its life, also, the 



lobster may lose a claw or an antenna. 



It is regenerated in two or three molts 



after the accident. The crayfish arid 



many other animals closely related to 



these two have the same power. 



The female lobster lays her eggs 

 usually during the summer months. 

 The eggs remain attached to the swim- 

 mere ts until the next spring, when 

 the embryos hatch. The larval lobster 

 (Fig. 70) immediately floats to the sur- 

 face, and for several weeks swims about 

 there. Its length at first is about eight millimeters (one third of 

 an inch). In general appearance it resembles the adult lobster, 

 except that the large thoracic appendages are two-branched 

 and the abdomen has no appendages. After the sixth molt the 

 lobster, then about two thirds of an inch long, has lost the outer 

 branches of the legs, has gained abdominal appendages, and is 

 nearly like the adult in other respects. At about this time the 

 young lobster leaves the surface, goes to the bottom, and 

 makes its way to well-protected places near the shore. 



FIG. 70. First Larval Stage 

 of American Lobster, 

 x 7. (After Herrick) 



