54 



LIVING CREATURES. 



cone is composed of whirls or whorls. The largest of 

 these is the body whorl (bw). Those above the body 

 are simply whorls which together form the spire (sp). 

 The opening at the base (;;/) is the mouth, the edges 



of which roll back on either 

 side. The name for each of 

 these edges of -the mouth is lip. 

 The lip on the right side of 

 the mouth in some of the 

 snail's large relations a very 

 broad lip is known by its sim- 

 ple name. That on the left 

 side is designated as the colu- 

 mella lip. Carefully break in, 

 on one side, the body whorl of 

 a common snail, and you will 

 see a little column rising from 

 the inside of this lip to the 

 apex like the column ' of a 

 spiral staircase. This little col- 

 umn is the columella, and its 

 outward fold is the columella 

 - lip. The lips of the snail's 

 shell are short and roll out 

 scarcely at all. The shell itself 

 shows that it has grown by constant additions, or sec- 

 tions, which have left their lines on the outside. 



Nothing could be more perfectly contrived for its 

 uses than this shell. When the animal retires within 

 it, the body must slip very easily up the spiral way 

 toward the apex. And when it is out and slowly 

 moving, what could be more compact and easily bal- 



Fiff. 8. Pond Snail Shell. 



