THE SNAIL 



385 



Body. — The body of the snail consists of a head, neck, foot, and 

 visceral hump. The head of a land snail {Helix) has one pair of 

 true tentacles which are probably sensitive to contact and smell, and 

 a pair of stalked ^'eyes" which can possibly detect different light 

 intensities, but are not sight organs. Our common genera of water 



Respiratory 

 apertum 



Velum 

 I 



A 



I I » 



GQnital aperture ' ^V^, 



Tentacle 



Mouth 



Respiratory aperture 



&qe of mantle 

 Foot — - 



stalked eye 



I 



I 



'Tentacle 



-Mouth 



Genital aperture 



Fig. 152. — Fresh-water and land snails with bodies expanded. A, fresh-water 



snail, Lymnaea; B, land snail, humboldtiana. 



snails {Lymnaea, PJiysa, Helisoma) have their eyes situated at the 

 base of the tentacles. Just in front of and below the tentacles is a 

 mouth. Located on the side of the head is the genital pore. The 

 broad muscular foot is covered with a mucus-secreting integument. 



