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TEXTBOOK OF ZOOLOGY 



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. 

 Just ventral to the mouth is the opening of the pedal gland which 

 deposits a highway of mucus over which the snail usually glides; 



Respiratory 

 aperturTz 



Velum 



A 



i I Mouth 



Genital aperture ' ^V^, 

 Tentack 



Respiratory aperture 



Jtaihed eye 



Edqe of wantle 

 Foot 



~1' 

 Genital aperture 



Fig, 134. — Fresh-water and land snails with bodies expanded. A, fresh-water 

 snail, Lymnaea; B, land snail, Humboldtiana. 



the gliding movements are scarcely perceptible. In some marine 

 snails the surface of the foot is covered with cilia, the latter facili- 

 tating movement. The visceral hump, which encloses the digestive, 

 circulatory, respiratory, excretory, and reproductive systems, is 

 protected by the shell which is lined with the mantle. A thick 



