.'300 FUNCTIONS AND INSTINCTS. 



shells or purples, I shall not have occasion to 

 dilate upon any of the remaining genera, but 

 shall merely notice a few peculiarities that some 

 of them exhibit. 



The Cowries are a tribe long known and 

 admired for their beauty and polish, and one 

 species 1 forms the current coin in many parts of 

 Africa, and many Asiatic Islands. Some re- 

 markable facts distinguish their history; from the 

 form of their shell and of its aperture, its incre- 

 ment could not take place in the usual way, 

 these animals, therefore, are furnished by their 

 Creator with a 'remarkably ample mantle, the 

 wings of which cover half the shell, and thus it 

 is gradually thickened, and changes and va- 

 riatioas in the colour take place that have 

 puzzled conchologists to distinguish a species 

 from a variety. At certain times the animal 

 is also stated to quit its shell, and form itself 

 a new one more appropriate to its size, a circum- 

 stance related by Aristotle of the Buccinum. 2 



Volutes are another polished tribe of shells, 

 which are probably formed by the mantle as in 

 the Cowries they are particularly distinguished 

 by having no operculum. The jet volute is 

 viviparous, and its young when excluded are 

 said to have shells an inch long. These pro- 

 bably are more exposed to enemies than the 



' Ct/j>r(ca Moncta. - Kiyptf, A list. 



