8 



(! aide to the Moll ii sea. 



Stbuctube. 



In nearly all the Mbllusca the body is divisible into three main 

 regions, the head, the foot, and the visceral sac which is covered 

 by the mantle. In the Lamellibranchia the head is hardly 

 developed at all. while in the Cephalopoda it is surrounded by 



Era. 2. 



g ■ ifeifel 



The " Glory-of-the-Sea ' Cone (Conns gloria-maris). Case 04. 

 (From the Philippine Islands.) 



and coalesced with the foot, the edges of which form a circle of 

 sucker-bearing arms. 



The foot is variously modified for creeping, digging, and other 

 purposes. In the Pteropoda or Sea-Butterflies the sides of the 

 foot are expanded to form large fins. 



The term mantle is sometimes restricted to the out-growing 

 folds at the sides of the bod}-, but is more correctly applied to the 

 entire covering of the visceral sac. The free folds may be re- 

 stricted in extent by coalescence with the body, and the cavity 

 they enclose may thus vary greatly in size and position. 



