SOFT-BODIED ANIMALS— THE MOLLUSKS 



279 



Class — Gastropoda 



The foot may seem a rather peculiar place to find an animal's stom- 

 ach ; yet that is where it is in the Gastropoda, a name which means 

 "stomach foot." However, the foot is about the biggest part of the body 

 of an animal in this class and is able to contain the stomach without 

 crowding. The snail is the best known example of this class. The 

 bilateral symmetry of snails is somewhat disrupted since the visceral 

 hump forms a spiral within the coiled shell. They creep along on the 

 foot at the traditional "snail's pace" which averages about two inches 

 a minute at full speed. However, their progress must be slow since 

 they slide along in a layer of mucus which is secreted by a gland at the 



Photo by Winchester 

 Fig. 19.8. A snail. Note the stalked eyes and the slimy appearance of the body. 



anterior end of the foot. The progress of any animal would necessarily 

 be slow if he had to spit and slide along as the snail does. The path- 

 ways of snails can be recognized by the silvery trails of dried mucus 

 which they leave behind. The land snails usually do their traveling 

 at night when the air is cool and moist. They withdraw their foot inside 

 the shell and seal the opening with mucus during the day so that their 

 bodies will not dry out. 



The snail has its eyes on stalk-like tentacles which can be extended 

 or retracted. These eyes do not see definite images as do human eyes, 

 but are capable only of detecting relative light intensities. 



A large species of snail is raised extensively in western Europe 

 for food. They are considered a great delicacy in France and can 

 even be purchased in some parts of the United States. There is no 



