SNAILS OF THE FOREST AND FIELD. 



The forest is the home of the snail, 

 where these interesting little animals may 

 be found by any one desiring a closer ac 

 quaintance. They are not generally easy 

 to find, being mostly nocturnal in habits 

 and remaining hidden away under leaves, 

 stones and old logs during the daytime. 

 On rainy days, however, they may be 

 seen crawling about, enjoying the deli 

 cious moisture. 



In our last article we reviewed a few of 

 the most interesting families of bivalve 

 shells, and in the present paper we desire 

 to draw the attention of the reader to the 

 order Pulmonata, which includes those 

 snails breathing air by means of a modi 

 fied lung. The snails differ from the clams 

 in having the body generally protected by 

 a spiral shell which is capable of contain 

 ing the entire animal. The former have 

 a more or less expanded creeping disk 

 which we call a foot, a head generally 

 separated from the body by a neck (the 

 reader will remember that the clams are 

 headless), and also a pair of rather 

 long eye peduncles protruding from the 

 top of the head, which bear at their tips 

 the round, black eyes, and a pair of short 

 tactile organs, or tentacles, extending 

 from the lower part of the head. The eye- 

 peduncles are peculiar in being invertible 

 in the same manner that a kid glove fin 

 ger is pulled inside out. 



The mouth is placed in the lower plane 

 of the' head and is recognized externally 

 as a simple slit. Inside of the mouth is 

 placed one ^of the most wonderful dental 

 apparatuses known to science. This is 

 called the radula, odontophore or tooth- 

 bearer, and is a belt of chitinous, trans 

 parent, yellowish or colorless material, 

 its upper surface being armed with nu 

 merous siliceous teeth arranged in longi 

 tudinal and parallel rows. The radula is 

 placed in an organ called the buccal sac 

 and occupies a position in the sac anal 

 ogous to that of the tongue in a cat or 

 dog, viz., on the floor of the mouth. It is 



formed from a layer of cells in the pos 

 terior part of the buccal sac, called the 

 radula sac, and new teeth are constantly 

 forming here to take the place of those 

 which have become worn by use. The 

 whole radula rests upon a cartilage, is 

 strongly fastened at the anterior end, and 

 is brought down between the two fleshy 

 lips of the mouth where it performs a 

 backward and forward movement, thus 

 rasping off with the sharp teeth particles 

 of food which have been cut into small 

 pieces by the horny jaw. During this 

 process the morsel of food is pressed 

 against the top or roof of the mouth. The 

 jaw is placed in the upper part of the 

 mouth in front of the radula, and is fre 

 quently armed with ribs to aid in cutting 

 or biting off pieces of food, as leaves or 

 vegetables. 



As before remarked, the radula is made 

 up of parallel rows of teeth, the whole 

 area being usually divided into five longi 

 tudinal rows, each row differing from the 

 one next to it. We have first a central 

 row, on each side of this a lateral row and 

 finally a marginal row. Each tooth in 

 each row is made up of different parts, a 

 basal part attached to the radula belt and 

 an upper part which is turned over or re- 

 flexed and bent backward so as to tear 

 off food particles by a backward move 

 ment of the whole apparatus. This di 

 versity of form in the teeth has led con- 

 chologists to adopt a tooth formula sim 

 ilar to that adopted for vertebrate ani 

 mals, so that the teeth of different species 

 can be compared and the animals classi 

 fied thereby. Thus each tooth has cer 

 tain prominences called cusps, which 

 vary in size, number and position, and 

 serve admirably to describe the different 

 groups of snails. All the mollusca, ex 

 cept the bivalves, are provided with this 

 radula. 



One of the most wonderful and inter 

 esting facts connected with the radula is 

 the large number of teeth on each mem- 



74 



