CKUSTACEA 



111 



Ecdysis. The periodical casting of the cuticle is of the 

 greatest importance in the life of the Crustacean. During 

 the instar material is accumulated, and this is brought into 

 use when the shell is shed. Before ecdysis the cuticle is sepa- 

 rated from the ectoderm and a gelatinous secretion invades 

 the space. The cells of the ectoderm are enlarged, they contain 

 glycogen, and they proceed to form a new cuticle. In the 



Chela 



FIG. 54. Larva of Nephrops. 



case of larvae which are changing their morphological charac- 

 ters the new formation involves the new structures associated 

 with the next larval stage. As has already been observed, 

 the ecdysis consists in the shedding of the old cuticle and its 

 internal prolongations. The back is raised, and pressure being 

 brought to bear on the thin region between the carapace 

 and the abdomen, this membranous part is burst, forming 

 an opening through which the Crustacean emerges. The 

 forward appendages are released, and the spines with which 

 that region is furnished are brought to bear on the old cuticle 

 in obtaining a purchase. Finally the rostrum reaches in this 

 way the hinder margin of the carapace, and the spines of the 



