ANATOMY AND PHYSIOLOGY OF A SNAIL. 15 



(/) The collar of Hie mantle, a portion of the mantle-edge just 

 visible beneath the aperture of the shell. Notice in this, on the 

 right side, the pulmonary aperture, the anus, and the external orifice 

 of the duct of the renal gland. 



(g) The pulmonary orifice, a large foramen situated on the right 

 side of the mantle-collar, and leading into the mantle cavity. 



(7z) The anus, opening side by side with, and slightly to the right 

 of, the pulmonary orifice. 



(/) The orifice of the duct of the renal gland, opening just inside 

 the pulmonary orifice. 



Kill the snail by drowning, and place in spirit for a few hours. 

 Twist the animal out of the shell, and replace it in the spirit. On 

 the shell note 



(a) The colour and markings. 



(b} Its conical shape. This may be discoid, as in Planorbis 

 complanatus ; oval, as in Amalia marginata ; or ear-shaped, as in 

 Testacella haliotidea. 



(c) Its division into four whorls, the largest being known as the 

 body-whorl. 



(d) The aperture, perisi^me, or peritreme, through which the snail 

 extends its prostoma. This is toothed in some species, as Pupa 

 secale, Vertigo pusilla, and Vertigo antivertigo. 



(e) The nucleus, or apex of the cone, the oldest part of the shell 

 corresponding to the umbo of the Lamellibranch shell. 



(f) The lines of growth, running parallel to the aperture. 



(g) The varices, numerous well-marked lines extending across 

 the body-whorl, and differentiating one year's growth from 

 another. 



(h) The columella, or axis around which the whorls turn. 



(*) The umbilicus, a foramen on the under surface of the shell, 

 opening into the cavity of the columella. 



(_/) In a hibernating specimen, notice the epiphragm, which com- 

 pletely closes the mouth of the shell. Examine with a lens its 

 under surface, and notice a small opening in its central portion 

 for the admission of air for respiratory purposes. 



THE SHELL GENERALLY CONSIDERED. The shell of the adult 

 Gastropod, with the exception of the internal shell of Arion and 

 Limax and the nucleus of Clausilia, is a secondary growth formed 



