HELIX. 265 
posterior angle from the upper coils, is the long tubular 
rectum terminating in the anus. 
Just inside this is a fine tube, the wrefer, leading from 
the excretory pore backwards to the &dzey. This is a large 
lobular dark-brown organ lying at the posterior 
angle of the cavity where the mantle joins the 
body. On its inner anterior side is an oval space with thin 
walls, the pericardium. ‘The kidney opens by a small aper- 
Blood. ure into the pericardium, which is a part of the 
Vascular, Colom, the kidney being regarded as a large 
* specialised nephridium. Inside the pericardium 
lies the eart, a two-chambered organ. The thin-walled 
Excretory. 
Fig. 186.—DIAGRAMMATIC MEDIAN SAGITTAL SECTION 
THROUGH THE HEAD OF A SNAIL. 
(In part after Howes.) 
Ocular Tentacle. 
Ocular Nerve. 
Brain. 
Salivary Duct. 
(Esophagus. 
Odontophore, 
Chitinous Upper 
Jaw. 
Opening of Pedal Gland. Retractor Muscle. 
Cartilage, Root of Odontophore. 
auricle receives blood from the pulmonary veins and pumps 
it into the ventricle. This, on contraction, propels the blood 
along a main aorfa, which passes into the body and divides 
into anterior and posterior arteries. The venous system 
consists of large lacunze or spaces around the organs. As in 
the Arthropoda, the body-cavity is a hemoccele or venous 
blood-space, the ccelom being only represented by the 
pericardium and possibly other parts. As in the lobster, 
the heart is systemic and receives blood from the breathing 
organs. 
