112 ESSENTIALS OF ZOOLOGY 



rostrum enable the creature to free entirely the forward part 

 of the body from the old shell. When this is accomplished 

 the tail is easily shaken off. The old cuticle is shed usually 

 in the complete state and falls into its original form. After 

 the ecdysis the new cuticle becomes hard and the ectodermal 

 cells sink once more into a flattened state. The other tissues 

 are also profoundly affected and only slowly recover. The 

 blood at once gains in volume through the action of the 

 digestive gland, and the result is that the new cuticle is 

 distended to the new size. The lime salts accumulated in 

 the digestive gland are liberated and undergo chemical change, 

 to be used in the hardening of the cuticle. The muscular 

 tissue takes a long time in recovering in the adult, when also 

 the gonads are in an immature and reduced state. 



The shedding of the cuticle produces a significant period- 

 ical loss, and the loss may be regarded as a special excretion. 

 It serves the purpose also of freeing the crustacean from the 

 varied life which obtains a lodgment on the cuticle. 



