BLOOD-VESSELS OF HALIOTIS. 



539 



aorta, the calibre of which is in this part as wide as a goose-quill ; it is 

 then seen that the large subcylindrieal basis of the tongue, which pro- 



Fig. 271 



Circulation of Haliotis (after Milne-Edwards). A, the head; B, the foot; C C, the two lobes of 

 the mantle ; D, mucus-secreting organ ; E E, 'the two branchiae ; r, the anus. Beneath the rectum, 

 that terminates at this outlet, is seen the orifice of the urinary apparatus ; and a little further back, 

 situated above the intestine, is the orifice of the generative apparatus. G, fold of intestine, which 

 is lodged in a special compartment of the abdominal cavity, separated from that containing the 

 stomach by a fibrous septum. H, the stomach, of which the anterior portion has been in a great 

 measure removed. I, pharyngeal cavity laid open. J, abdomen. 



a, aortic ventricle surrounding the rectum. 



6, the left auricle, into which opens the efferent vessel of the corresponding branchia, a portion 

 of which is shown at E. The right auricle is seen immediately beneath the ventricle, and the 

 corresponding branchia has been raised in order to show throughout its entire length the 

 branchial vein or efferent canal, E, which runs along the adherent margin of the branchia, and 

 brings arterialized blood from that organ to the heart. 



c, the great aorta, which arises from the posterior extremity of the ventricle and runs forward 

 between the stomach and the intestine to discharge itself into the cephalic cavity. 



d, the abdominal artery, or posterior aorta, which arises from the commencement of the aorta 

 and foil ows the convolutions of the intestine, to which, as well as to the liver, it furnishes branches. 



e, arterial sinus, into which the aorta empties itself. This is a great cephalic lacuna, limited 

 above by the parietes of the pharynx, in front by the integuments and muscles of the head, and 

 posteriorly by fibro-cellular bands. On injecting the animal by this cephalic chamber, the whole 

 arterial system is immediately filled. 



f, the great artery of the foot, which arises from the cephalic sinus, and soon divides into four 

 branches, which extend towards the hinder part of the foot. g, one of its lateral branches. 



h, afferent vessel of the left branchia. A little in front of the heart is seen the transverse canal, 

 or common venous reservoir of the branchia, which unites this vessel with its fellow, and which 

 receives the veins from the rectum. 



i i, veins of the two lobes of the mantle in communication with a capillary network that extends 

 along the base of the branchiae, and is proceeding to anastomose with the branchio-cardiac vessels. 



fc, efferent vessels from the urinary gland opening into the common venous reservoir of the 

 branchiae. 



I, venous canal of the shell-membrane or partition that extends from the walls of the abdomen 

 to the margin of the shell. 



TO, hepatic veins proceeding to open directly into the free space which surrounds the intestine, and 

 which is continuous with the rest of the abdominal cavity. On the posterior part of the foot are 

 seen veins which open into a system of lacunae situated upon the median line, and communicating 

 with the abdominal cavity. 



