PHYLUM ARTHROPODA 



also a means of getting rid of an old worn-out coat and acquiring 

 a new one. The young stay with the mother for about one month, 



B 



FIG. 207. Stages in the development of the egg of the crayfish. A, super- 

 ficial cleavage of the egg. B, embryo in the Nauplius stage. A, anus; 

 a 1 , antennule; a' 2 , antenna; e, rudiment of eye; /, upper lip; m, mandible; 

 ta, thoraco-abdominal plate. (From Korschelt and Heider, after Reichenbach.) 



and then shift for themselves. They molt at least seven times 

 during the first summer. The life of a crayfish usually extends 

 over a period of three 

 or four years. 



Regeneration. - - The 

 crayfish and many ^ 

 other crustaceans have fj_ 

 the power of regenerat- \jL 

 ing lost parts, but to a 

 much more limited ex- 

 tent than such animals 

 as Hydra and the earth- 

 worm. Experiments 

 have been performed 



Upon almost every one FIG. 208. Diagram showing antenna-like 

 Of the appendages as organ regenerated in place of an eye of Pa/ . 



(From Morgan, after Herbst.) 



well as the eye. The 



growth of regenerated tissue is more frequent and rapid in 

 young specimens than in adults. The new structure is not 

 u 



