56 



Lessors in Zoology. 



by making a door of the mucus, or slime, that comes 

 from their foot. Every year when cold weather comes, 

 the land snails hide away under the roots of a tree, or 

 under a log or stone, and make this door to shut them- 

 selves in. Most of the water snails have a door all the 

 time, which they can shut whenever they please. 



Lesson II. 



Jnst before the leason we drop onr Bnaila into a bowl of warm 

 water, and they are soon coming ont, foot foremost. 



Holding them upside down, we see a fleshy rim around 

 the aperture. This is the mantle, which builds the shell- 

 Just under the edge of 

 the shell is the breathing- 

 hole (Fig. 4, b), which 

 keeps opening and shut- 

 ting, and leads into the 

 snail's simple lung, only 

 a sac in the mantle with 

 blood-vessels in its sides. 

 The breathing-hole is on 

 the right side when the 

 aperture points toward the right, and on the left when 

 that points to the left. 



Two pairs of horns, that are gradually pushed out, are 

 the tentacles (Fig. 4, s ^ and i t). The long tentacles are 

 the eyestalks ; the others are used only as feelers. We 

 touch a long tentacle, and a black thread pulls the eye 

 down inside. The black thread is the lining of the ten- 

 tacle, which contains muscles that draw the end in just as 

 we turn the finger of a glove when we pull it off in a 

 hurry. 



The snail moves on its broad foot, and by putting it on 



