VII 



MOLLUSOA—THE FOOT AND ITS GLANDS 



109 



saltatory Strombidai, is clear. The sole of the foot in Oxygyrus, although it can be 

 used for creeping, is looked upon as a sucker. 



In Atlanta (B), the arrangements of the foot are similar to those in Oxygyrus, 

 but the iin-like outgrowth of the propodium has become its most important part, 

 the comparatively reduced sole or sucker appearing merely as an appendage to it. 



In Oarinaria (C) both the foot and the general external appearance of the whole 



Fio. 99.— Comparative Morpliology of tlie Heteropoda. A, Oxygyrus. B, Atlanta. C, 

 Carinaria. D, Pterotrachea 9 , adapted from figures by Souleyet. 1, Visceral dome and shell ; 

 2, head with eyes and tentacles and proboscidal snout (3) ; 4, gills ; 5, foot with sole, which latter in 

 B and C is rednced to a sucker, and in D is wanting ; 6, fin-like appendage of the foot ; 7, meta- 

 podium with, 8, operculum. 



animal are much changed. The metapodium, which here has no operculum, appears 

 as a mere tail-like posterior prolongation of the body. The fin is much broader and 

 longer, and the sucker seems to have shifted backward along its free edge. 



Finally, in the Pterotrachea (D), the sucker (the original sole of the foot) is still 

 further reduced, and only present in the male. 



The Heteropoda are said to attach themselves occasionally by means of the sucker. 



2. Pulmonata. 



The foot is here almost always undivided, and provided with a, large flat sole 

 for creeping. In a few Aurieulidce, however [Melampus, Leuconia, Blauneria, 

 Fedipes), it is divided into two portions by a. temporary or permanent transverse 

 groove. 



3. Opisthobranchia. 



In almost all Opisthobranchia the foot has a well-developed sole for creep- 



