CHAPTER IT, 



THE ANATOMY AND PHYSIOLOGY OF A SNTATL. 



PAKE a live Wrinkled Snail (Helix aspersd] or Roman Snail 

 (Helix pomatia), and allow it to crawl along a piece of paper 

 before you. Note 



1. That pait only of the animal is extruded (prostoma), the 

 other portion (metastoma, or visceral hump] 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 (dorsal tentacles, or ommato Chores), are much longer than the 

 lower pair (ventral tentacles). 



(b} The mouth on the anterior extremity of the head segment, 

 bounded by a circular and a lateral lip. 



Pe 



Fig. 3. Helix pomatia. O, ommatophore ; Pe, foot. 



(c) 1\\zfoot, 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. 



