VII 



MOLLUSC A THE FOOT AND ITS GLANDS 



109 



saltatory Strombidce, 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 fin-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 Carinaria (C) both the foot and the general external appearance of the whole 



FIG. 99. Comparative Morphology of the 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 reduced 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 PterotracJiea (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 Auriculldce, however (Melampus, Leuconia, Blauneria, 

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

 groove. 



3. Opisthobranchia. 

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



