INTRODUCTION. XX111 



not be again secreted, in sufficient quantity, till after 

 the snail has had time to recruit its strength by food. 



What has been said, it is presumed, will be suffi- 

 cient to explain the different phenomena, which the 

 colours of shells in general present ; but there exist 

 some genera, such as Voluta, and Cyprcea, which are 

 painted by a process with which Reaumur was un- 

 acquainted. Their colours are disposed on two 

 parallel surfaces, the exterior of which is produced 

 by a particular organization of their animals, and is 

 the result of an operation described by M. Bru- 

 guiere, and noticed in the preceding section. 



The shell of the cowry receives its colour from the 

 pores of the animal at two distinct periods, and by 

 different ways. In the first place, that part of the 

 shell is formed, which is immediately secreted from 

 the collar, or the body, of the animal; this coat is 

 of a moderate thickness, much inferior in strength to 

 what it acquires in the sequel. In this primary ope- 

 ration, there is nothing peculiar from what takes 

 place in other shells ; but above this coat, on the 

 convexity of the shell, there is formed a second, 

 which covers the first entirely with a compact sub- 

 stance, in some places very thick, and generally 

 stained with different colours. The organs which 

 deposit this second bed are two soft membranaceous 

 wings, which, issuing from the mouth of the shell, 



