TAYLOR : LIFE HISTORY OF HELIX ASPERSA. 103 



The outermost rows or marginals are low and wide, bearing 

 one outer bifid cutting point, and a second — sometimes bifid — 

 side cutting point. 



Digestive Organs. The mouth lies at the anterior end 

 of the body. We find here a structure characteristic of the 

 whole group of the Odontophora, viz., the tongue which is 

 attached to the floor of the mouth. This apparatus, lying in 

 what is called the buccal mass, consists of a skeleton ; of a sub- 

 radular membrane, which is continuous with the lining of the 

 oral cavity ; of the radula or lingual ribbon ; and of intrinsic 

 and extrinsic muscles. The food, after having been subjected 

 to the rasping action of the radula as well as to the saliva, finds 

 its way into the oesophagus. The succeeding enlarged portion 

 of the alimentary canal has often been termed the ' proventri- 

 culus,' and on it we find two well-developed salivay glands 

 whose ducts open into the buccal mass. The proventriculus 

 is only distinguishable from the stomach by a slight indenta- 

 tion. The intestine leaving the stomach coils round several 

 times, being quite enveloped in the large brownish-coloured 

 liver. It ultimately passes along the respiratory chamber, the 

 anus opening at the respiratory orifice. There is also a kidney 

 in close proximity to the heart. 



Respiratory Organ. Aerial respiration is effected by 

 the walls of a pulmonary chamber which is a modification of 

 the pallial cavity. Air enters by the respiratory orifice and the 

 blood which finds its way into the numerous vessels in the 

 mantle-roof is thus purified. 



Circulatory System. As in most of the odontophora 

 there is a single auricle and ventricle in the heart. The puri- 

 fied blood is collected from the respiratory chamber into one 

 large blood-vessel which sends its contents to the auricle. 

 Every contraction of the auricle forces a stream of blood to the 

 ventricle which again propels it into a main efferent vessel. 

 This soon divides into two branches — the hepatic artery and 

 the aorta, one supplying the viscera and the other the anterior 



