192 AN INTRODUCTION TO ZOOLOGY. 



(fig. 54). The hermit-crab {Pagurus) belongs to the 

 Macrura, and has a soft tail ; hence it has to live in: 

 the empty shell of a univalve. These crabs are very- 

 amusing. If two are put in the same basin of sea- 

 water they instantly go for one another ; the stronger 

 will turn the other out of his shell, and try it on ; but 

 as the stronger is usually the bigger, he mostly leaves 

 it for his own, and lets the original owner go back to 

 it. Indeed, the fight seems to arise according to the 

 principle enunciated by Sir Arthur Helps, that "Every 



Pig. 54.— Zoea or larval stage of tlie common Shore Crab, Carcinus Mcenas. 



man thinks every other man's bread-and-butter is 

 nicer than his own," i.e. every hermit-crab thinks 

 every other hermit-crab's shell is nicer than his own, 

 until he has an opportunity to try it, and convince 

 himself of the contrary. The fact is, that since a 

 new shell is very necessary as the crab grows, and is 

 not always immediately to be found, a new shell is 

 the summum bonum of hermit-crab existence, and the 

 belief that his own shell is too tight is a fixed idea. 



