BAKER: FIELDBOOK OF ILLINOIS LAND SNAILS 5 



find snail shells ot several different sizes. Some are globular like 

 weed seed; others are elongated like the seed of grass. Some are 

 brown or blackish; others, horn-colored or yellowish. Some are 

 opaque; others, almost transparent, like paraffin. One has 

 stripes; another, spots. 



Slugs. — Not all snaillike animals have shells into which 

 they can retire. Under our log we find one apparently without a 

 shell. This is known as a slug, page 129. It is black in color, 

 about an inch in length, and it has a peculiar shieldlike pro- 

 jection near the head. Under its shield we find a small, flat shell 

 which acts as a protection to the breathing organ. Another slug, 

 a different kind, is about 3 inches in length, of a whitish color 

 covered with black spots, and has no shieldlike projection near the 

 head. This slug is always covered with mucus and when handled 

 exudes great quantities of this matter. Only five species of slugs 

 are common in Illinois. 



Food and Feeding Habits of Snails 



If we place one of our Illinois woodland snails in a glass jar 

 and permit it to crawl up the side, we may observe that it has on 

 the under surface of the head a mouth, which repeatedly opens 

 and closes. When we look closely we see a rough, tonguelike 

 object which is pushed out of the mouth and pulled in somewhat 

 like a cat's tongue in lapping milk from a saucer. This is the 

 radula or tooth-bearer with which the snail obtains its food. 

 When the snail is crawling up the side ot a glass jar, we may 

 observe this tongue licking up the particles of vegetable matter 

 on the glass, or if we place a piece of lettuce in the jar we may see 

 the animal biting off with its \\orwy jaw small pieces of the lettuce 

 which it then scrapes into smaller pieces with the radula. 



The mouth parts. — If we cut a longitudinal section from 

 the head of a dead, preserved snail, we may see the relationship 

 of the radula to the other parts of the head and mouth. Such a 

 section is shown in fig. 2. The ribbonlike radula of our woodland 

 snail is drawn over a part of the mouth called the cartilage. 

 Different muscles move the cartilage and the radula backward 

 and forward, allowing the snail to rasp off particles of food 

 brought down between the lips. The radula wears out at the 

 anterior or front end, which is used more than any other part. 

 To repair this wear, the whole radula grows forward from the 

 core, much as our finger nails grow from their bases. 



