52 



GENERAL ZOOLOGY 



cuticle through the agency of epidermal cells. The epidermal 

 layer lacks a basement membrane, and the lateral walls of the 

 cells are poorly defined. 



conn, t 

 nu. 



mvs.c. 



Fig. 28. — Portion of the new integument of a lobster, Homarus, as seen in 

 section. The cuticle is shown above in stratified layers, conn.t.nu., connec- 

 tive-tissue nucleus; bl.c, blood cells; mus.c, muscle cells. (From Dahlgren and 

 Kepner, Principles of Animal Histology, The Macmillan Company. By 

 permission.) 



Animals with a hardened cuticle undergo periodic molting 

 or ecdysis, during which the cuticle splits in definite places and 

 the animal crawls out. The new cuticle is then secreted, and 

 while it is still soft and elastic, the animal grows in size. A 

 soft-shell crab is one that has recently shed its cuticle. 



