The anatomy of Lottia gigantea Gray. 29 



The great circumpallial blood sinus which conducts the aerated 

 blood to the auricle is best considered with the venous circulation. 



Venous circulation. The blood which is collected from the 

 various organs of the body reaches for aeration, the ctenidium and 

 mantle, the latter being the most important respiratory organ. From 

 these two structures it is carried to the heart. Blood to the pallium 

 may either come directly, as is the case with the greater part of that 

 of the foot and gonad, or it may pass through the meshwork of vessels 

 of the kidney, as happens with the blood from the visceral artery. 



The venous sinuses of the foot are shown in Figs. 19 and H. 

 They are greater in calibre than any of the arteries of the foot, 

 with the exception of the pedal arteries. Their course, which is 

 somewhat devious, and in several planes, is best understood by a 

 comparison of the two figures. About twelve of these vessels are 

 present corresponding to the rather constant number of veins piercing 

 the shell muscle and leading from the kidney blood sinus to the 

 mantle. A prominent branch results from the anastomosing of numerous 

 sinuses in the lower parts of the foot. This passes upward and 

 joins another branch or branches which come from the central portion. 

 These divisions in the central part of the foot lie above the neural 

 artery (Fig. H, in white) and communicate with each other by rather 

 irregular and fairly large sinuses, and also by much smaller ones. 

 Into these sinuses many small arteries open directly. Transverse 

 venous sinuses are also in communication with the median longitudinal 

 sinus already spoken of under the circulation of the gonad. Each 

 vessel which results from the union of branches from the lower parts 

 of the foot, and those from the median portion, courses upward and 

 outward, to open into the transverse vessel leading from the kidney 

 vein to the mantle (19). The median sinus, though classed with the 

 pedal circulation by reason of its connection with very numerous cross 

 sinuses lying within the muscular tissue of the foot, itself, of course, 

 lies at the base of the membrane separating the coelom from the 

 right kidney, and along with the other vessels in this membrane, may 

 be said to be a definite lacunar space between the exceedingly thin 

 epithelium lining the coelom, and the thicker epithelium lining the 

 kidney cavity. The two epithelial linings are hence fused to form one 

 membrane. In the diagram of the venous circulation of the foot only 

 the more prominent vessels have been shown. 



So far as I have been able to observe, all the blood from the 

 visceral artery reaches either the mantle or the gill by way of the 



