Animal of pond snail (Lirnnfea mighelsi). 

 bp, breathing pore ; e, eye : f, foot ; h, head ; 

 s, shell ; t, tentacles ; v, vela, or lateral lobes 

 of head. 



While we were examining one of these shells, the occupant thereof 

 was twisting itself about in a vain effort to find some object upon which 

 it might crawl. This gave us a splendid opportunity to examine the 



animal. Its color was dark horn, 

 with a bluish tinge on the head. 

 The foot was very broad and flat, 

 and separated from the head by 

 a little constriction. The head was 

 very broad, and widened at the 

 sides into two lobes, called vela. 

 The tentacles were short and tri- 

 angular, and on swellings at their 

 inner base the little black eyes 

 were placed. Just at the edge 



of the shell, the little hole through which air enters the lung could 

 be seen opening and closing. 



u We must understand," said the Professor, " that the snail cannot 

 leave his house or shell any more than the turtle can crawl out of its 

 shell. The animal of the pond snail is fastened to the coluniella by 

 a huge coluniella muscle, which grasps this part of the shell and holds 

 it fast. A part of the animal, called the mantle, is kept in close con- 

 tact with the shell by means of small muscles called sphincter muscles. 

 It is the edge of this mantle, called the mantle collar, which secretes 

 the shelly matter and builds up the shell. It also provides the beauti- 

 ful colors seen in shells which are found in the tropics. We must 

 thoroughly understand that were we to take the animal from its shell, 

 it would die. 



" The animal, when removed from the shell, is seen to be the exact 

 counterpart of it, and it is also seen to be covered with a soft mem- 

 brane, the mantle, which is molded to the shell. The spire is mainly 

 occupied by the enormous liver. 



"You will remember," continued the Professor, "that we spoke 

 of the clams as bivalves because they had two shells. The snails are 

 called univalves because they have but one valve, or shell, which is gen- 

 erally in the form of a spiral, as you have already learned. All snails 

 are not univalves, however, as you may observe when you visit the 

 museum. Some snails have the shell composed of several pieces, while 

 other snails are without a shell." 



Placing the pond snails in our collecting pail, we then looked for 

 other molluscan inhabitants of the river. Just a little way from the 

 shore, several large pond snails could be seen apparently crawling on 



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