posterior angle from the upper coils, i^ 



rectum terminating in the anus. •--.,^.^^^ 



Just inside this is a fine tube, the ureter, leading ^ 



the excretory pore backwards to the kidney. This is a large 



lobular dark-bre'wn 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- ^^^^ ^^^^ ^^ pericardium, which is a part of the 



coelom, the kidney being regarded as a large 



specialised nephridium. Inside the pericardium 



lies the hearty a two-chambered organ. The thin-walled 



Fig. i86. — Diagrammatic Median Sagittal Section 



THROUGH the HeAD OF A SnAIL. 



(In part after Howes.) 



Ocular Tentacle. 



Ocular Nerve. 

 Brain. 



Salivary Duct. 

 .CEsophagus. 



Odontophore. 



Chitinous Upper 

 Jaw. 



Opening of Eedal Gland. \ \ Retractor Muscle. 



Cartilagf,. Root of Odontophore. 



auricle receives blood froni the pulmonary veins and pumps 

 it into the ventricle. This, on contraction, propels the blood 

 along a main aorta, which passes into the body and divides 

 into anterior and postd rior arteries. The venous system 

 consists of large lacunae ot spaces around the organs. As in 

 the Arthropoda, the body-cavity is a haemocoele of venous 

 blood-space, the coelom beirig only represented by the 

 pericardium and possibly oth(^r parts, M in the lobster, 

 the heart is systemic and receives blood 'from the breathing 

 organs. \ 



