LAND SNAILS. 17 



end containing the eye disappears first, as the end of a glove- 

 finger disappears, when the hand is withdrawn from the 

 glove, the glove turning wrong-side out. 



A B 



Fig. 19.— Showing Snail with Temtacles eetracted, A ; and Tentacles pboteuded, B. 



16. Something may now be learned as to the way in 

 which land snails eat. 



By placing before the snail the tender leaves of lettuce or 

 cabbage, the head will be seen to move, as little mouthfuls 

 of the leaf are bitten ofE. The upper lip of the mouth is fur- 

 nished with a hardened piece called the iuccal plate. It is 

 crescentic in shape, and, in some species, the cutting edge is 

 notched, so that it acts like an upper set of teeth, by which 

 it bites ofi little bits of the leaf. The floor of the mouth 

 is lined by a membrane having upon it rows of little points 

 which enable the snail to rasp and grind its food. These parts 



Fig. 20.— Jaw, oe Bpccal Plate of a Land Snail, highly magnified.— {It can just he 

 discerned without a microscope.) 



are so minute that they can be studied only by the aid of a 

 microscope. If the pupil will watch his fresh-water snail 



