124 



THE SNAIL. 



A. The Walls of the Mantle-cavity. 

 1. The roof and sides of the cavity are formed by the 

 mantle itself, a thin fold of skin which bears on its 

 under surface a very rich network of large blood- 

 vessels, especially abundant in front and along the 

 right side. 



r ^* These vessels, in which the blood is aerated, unite 

 to form a large trunk, the pulmonary vein, which 



Fio. 31. Helix pomatia. Dissection from the right side to show the 

 mantle-cavity and organs in relation with it. The arrow passes 

 through the pulmonary aperture into the mantle-cavity. The shell 

 and the upper part of the spiral visceral mass have been removed. 

 (a. m. m.) 



A, auricle. B, anus, c, collar. D, dorsal body-wall forming the floor of 

 the mantle-cavity, e, eye. F, foot. G, genital aperture. H, groove leading 

 to genital aperture. K, kidney. |_, lip. P, pulmonary vein. PA, pulmonary 

 aperture. PC, pulmonary or mantle-cavity, pv, pulmonary vessels in root 

 of mantle-cavity, pv', cut ends of pulmonary vessels. R, rectum. S, anterior 

 tentacle. T, posterior tentacle, u, ureter. V, ventricle. 



takes back the oxygenated blood to the heart, run- 

 ning along the left side of the kidney (see p. 139). 



The mantle is greatly thickened in front to form 

 the collar : posteriorly it is thickened by the kidney 

 and pericardium, both of which he in its substance. 



