XXXIV INTRODUCTION. 



The necessity for the process in question is so evident 

 seeing that, without it, there would be no possible means 

 of allowing the gradual growth of the animal, that it is 

 matter of surprise that it should have ever been doubted, as 

 it appears to have been by a distinguished entomologist, 

 more especially of late years, when so many conclusive 

 observations have been made of the fact. There is no 

 doubt that in many of the higher forms it takes place 

 annually, with great regularity,* until the growth is com- 

 pleted, which in many species is not the case before the 

 animal is many years old. This is proved by the extent 

 to which the size increases by each moult, compared 

 with the difference between the young and the old ani- 

 mal ; and it is evident that after the growth has reached 

 its maximum the crust ceases to be changed, from the 

 fact which I have seen in several instances, as in the 

 common crab, the lobster, and some others, where the 

 carapace of the still living creature was the seat of bar- 

 nacles so large, that several years must probably have 

 been required for attaining their existing size. 



The observations of Reaumur to which I have alluded, 

 and those of subsequent naturalists, and especially of 

 Mr. Couch, furnish us with the following history of this 

 curious process. 



When the animal by gradual internal increase has 

 become too large for its existing covering, it ceases for a 

 time to feed, and retires to a secret and undisturbed situa- 

 tion, where it may undergo the process in security. If it 

 be examined at this time, an evident loosening of the 



* Some recent observations by Mr. Warrington shew that in the common 

 prawn, the moult is much more frequent ; he has noticed its occurrence with 

 much regularity, every twelve clays, in the snmmcr. 



