60 Invertebrate Zoology. 



back, the canal being directed forward, the spire backward. 

 The opening of the shell is then on the right side. 



Examine an animal that has been removed from the shell, 

 and compare the number of whorls made by the body with 

 the same of the shell. 



The lower surface of the foot is somewhat wrinkled. It 

 has, leading from its centre, an opening from the "pedal 

 gland" At the posterior and dorsal p^rt of the foot, observe 

 the attachment of the operculum. Extending anteriorly and 

 dorsally, the substance of the foot merges into the head. 

 The head is anteriorly provided with two laterally projecting 

 and triangular flaps, the tentacles^ Midway between the 

 tentacles, but somewhat below them, is the opening of the 

 mouth. Frequently the elongated proboscis projects from the 

 mouth as a flexible tube, an inch or more in length. If the 

 specimen being examined is a male, the large introraittent 

 organ, or penis, will be observed. It is situated a little to 

 the right of and above the right tentacle. 



The collar is a circular fold of the mantle that entirely 

 surrounds the body just posterior to the head. In life, it 

 was applied to the lips of the shell, and by its activity the 

 body of the shell (middle layer as well as the epidermis) 

 was elaborated. At a point corresponding to the canal the 

 inner part of the collar is produced into a groove-like siphon. 



If the collar is elevated along its antero-dorsal portion, a 

 large chamber, the mantle cavity, will be exposed. 



The soft parts of the animal, extending into the spire, are 

 collectively spoken of as the "visceral mass. 1 ' 1 It should be 

 borne in mind that the outer surface of each whorl corre- 

 sponds to the left side of the animal, while the inner surface, 

 next the columella, is the right side. 



1 On the lateral edge of each tentacle is the small deeply-pigmented eye. 



