CLASS GASTEROPODA. 



65 



observe that it is a slug-shaped animal, which walks, or 

 rather creeps about, upon the lower surface of its body, 



Fig. 27.— A, Sketch of a Whelk iBuccimim undatum) in motion ; / Foot; 

 h Head earning the feelers (0 with the eyes (e) at their bases ; p Pro- 

 boscis ; s Respiratory siphon, or tube by which water is admitted to tlie 

 gills ; o Operculum. B, Shell of the Whelk : a Spire ; 6 Body-whorl ; 

 n Notch in the front margin of the mouth of the shell : m Outer lip of 

 the mouth of the shell. This figure is half the natural size. C, A small 

 cluster of the egg-capsnles of the Whelk. (B and C are after Wood- 

 ward.) 



carrying over its back a shell composed of a single piece 

 (fig. 27, A). The surface upon which the animal creeps 

 forms a flattened and very muscular disc, which is tenned 

 the "foot" (fig. 27, A,/). In front the animal ex- 

 hibits a very distinct head (h), which carries a pair of 

 extensible processes (t), the purpose of which is to act as 

 " feelers," or organs of touch. At the bases of these 

 feelers are situated the two eyes, in the form of small 



