376 



Transactions. 



ventricle is of more definite and constant shape than the auricle ; from 

 above it is broad at the auricular end and tapers to the other extremity, 

 where it ends in a blunt point. After removal of the auricle the valves 

 can be seen partly open, leaving the silt-like orifice through which the 

 blood passes to the ventricle. When the ventricle contracts, the lips of 

 these valves come together and close the passage. This action can be 

 well seen by filling the chamber with water and gently squeezing it. The 

 walls of the ventricle are stout and muscular, and from the exterior can be 

 seen the multitude of muscular fibres running in varying directions in 

 them. Most of the fibres converge on a stout ring formed round the exit 

 of the aorta ; their other ends, often branched, are attached to the walls. 



Arteries. 



The aorta leaves the ventricle near the middle of its ventral side, and, 

 piercing the pericardial wall, to which it is firmly attached, takes a course 

 almost directly transversely towards the 

 right and a little backwards, passing be- 

 tween the anterior lobes of the digestive 

 gland till it reaches the intestine. At this 

 point it bifurcates, giving rise to the cepha- 

 lic aorta (fig. 1, c.a.), supplying the anterior 

 region of the body, and the visceral aorta 

 (r.a.), supplying the posterior organs. This 

 passes backwards among the lobes of the 

 digestive gland, and divides into three main 

 branches, which carry blood to that organ, Q^ a |^ 

 to the hermaphrodite gland, intestine, and 

 posterior end of the stomach. For the pur- 

 pose of studying the distribution of the 

 arteries I injected coloured " starch injec- 

 tion " into the ventricle, and was successful 

 in obtaining a beautiful preparation showing 

 even the smaller branches, but could not 

 afi'ord time, nor did I consider it worth 

 while, to work out the distribution of the 

 visceral aorta in further detail. 



The cephalic aorta passes to the right 

 over the dorsal surface of the viscera, and 

 comes in contact with the body-wall (i.e., 

 the floor of the pallia] chamber) just below 

 the kidney. Continuing its course to the 

 fight, it curves forwards till it reaches the 

 spermothecal duct, in front of which it Arteries on the ventral aide of 

 passes downwards and forwards on to the stomach; 4. b.a., superior 

 floor of the body -cavity. Just before reach- 

 ing this point it gives off the genital artery 

 (gn.a.), which, passing backwards, supported 

 by a thin membrane, gives rise to the vessels 

 of the spermotheca and genital duct. The cephalic aorta now runs forwards 

 for a short distance on the floor of the body-cavity, and after giving off 

 a vessel (w.a.) which disappears into the muscles of the right body-wall 

 and foot it turns to the left and reaches the nerve-collar, through which 

 it passes below the oesophagus. 



Fig. 2. 



buccal artery : g.b.a., gastro- 

 buccal artery; g.a., gastric 

 artery ; oc, oesophagus ; st., 

 stomach. 



