CHAPTER II. 



THE ANATOMY AND PHYSIOLOGY OF A SNAIL. 



Take a live Wrinkled Snail [Helix aspersd) or Roman Snail 

 {He/ix poniatia), and allow it to crawl along a piece of paper 

 before you. Note — 



1, That part only of the animxl is extruded (prosfonia), the 

 other portion {meta stoma, or visceral Jiiiiup) being permanently 

 lodged within the shell 



2. On the prostoma note — 



{a) The head segment^ forming its anterior extremity, and bearing 

 two pairs of processes or tentacles ; the upper pair, carrying the 

 eyes [doi'sal tentacles^ or of/ujiatopiiores), are much longer than the 

 lower pair {I'entral tentacles). 



{b) The moutJi on the anterior extremity of the head segment, 

 bounded by a circular and a lateral lip. 



Fig. 2>-— Helix poiiiatia. O, ommatophore ; Pe, foot. 



(c) ThQfoot, forming a well-marked muscular expansion on the 

 under surface of the prostoma. 



{d) The orifice of the pedal gland, between the mouth and the 

 foot. 



{e) The genital orifice, slightly below and slightly behind the 

 right dorsal tentacle. 



