50 



distinot spaces running bark tlirnugh the font on either 

 side just internal to the nerve cord. The anterior sinus 

 opens into these near the pedal ganglia. 



(h) Spaces in the visceral hump, from that part of the 

 sinus which surrounds the radula. 



The foot is, therefore, supplied from the anterior aorta 

 via the anterior sinus, while the visceral hump is supplied 

 partly in the same way and partly by the posterior artery. 

 The shell muscle seems to be furnished with blood from 

 the pedal sinuses. The impure blood from the foot and 

 that from the visceral hump goes to the perivisceral 

 sinus whicli, as its name implies, surrounds the viscera. 

 From this sinus some of the blond goes to the blnnd 

 spaces in the trabeculse, etc., of the large right kidney, 

 and, more doubtfully, to those of the left kidney. For 

 this reason the perivisceral sinus and large kidney are 

 about co-extensive. Practically the whole of the blood 

 from the perivisceral sinus, including that which has 

 traversed the kidney trabeculse, etc., ultimately finds its 

 Avay out to the mantle. Some of it goes to the nuchal 

 mantle, while the remainder reaches the mantle skirt 

 by way of channels running between the fasciculi of the 

 shell muscle. 



Before describing the oxygenation of the blood, it is 

 convenient to describe the circulation in the head, in 

 the nuchal mantle, and in the left kidney. The main 

 channels in the head region are the parts and ramifications 

 of the anterior sinus, i.e., spaces below the lining epithe- 

 lium of the gut, and pai"ticularly of the odontophore. 

 From this space, blood seems to go all over the head 

 around the body wall. The inner lips, which are 

 puckerings of this gut epithelium and subjacent tissue, 

 contain each a blood space so that their opening and 

 closing may be brought about in part by changes in blood 



