156 NATURAL HISTORY OF OUR SHORES 



While on the subject of " Morphology " (study of form) 

 we had better glance over another important matter in 

 crab life. This is the moulting, or change of shell Ecdysis 

 is the term used to express it. 



While encased in its firm shell a crab is not seen to grow 

 the shell is a " fixed quantity " but the crab is growing 



Fig. 64. Common Shore Crab, f Natural size 



within, in a state of compression, until, by-and-by, the 

 situation becomes awkward and something must be done. 

 The shell opens at the joint between the carapace and 

 the abdomen or " tail," arid the crab, covered only with a 

 leathery skin, and elastic as a bag of jelly, withdraws from 

 its tight jacket, and is about one third larger than this old 

 garment. It seeks a place of shelter, for it is aware of its 

 vulnerability, and remains there, still growing, for a day 

 or two, until the cuticle of its skin shall have secreted lime 



