Metamorphoses of Cmstaceans. 105 



higher crustaceans is transitory, and sometimes is 

 passed over before the embryo leaves the egg, and in 

 crabs the form assumed by the newly hatched young 

 is that of a small shield-covered body with two eyes 

 and long jointed abdomen (fig. 57, A) ; this curi- 

 ous larva is called Zoea, and by the shortening of its 



FIG. 59. 



Pennella, parasitic on the Sunfish. A, Entire animal, 

 half real size ; B, head. 



tail and the vanishing of its dorsal spine, it becomes 

 changed into its adult form. 



All crustaceans undergo successive moultings or 

 changings of shell, and during these changes lost parts 

 become restored and the several changes in meta- 

 morphosis can be seen at these periods. Crustaceans 

 part with their limbs easily under circumstances of 

 fright or seizure ; thus if a limb be taken hold of 

 forcibly the animal will probably break it off between 

 the first and second joints in its efforts after freedom. 

 At the next moult, there appears a new limb budding 

 on the soft uncovered body, and when the new shell 

 forms and hardens, a small limb is seen in place of 

 the lost one. 



