CIRCULATORY SYSTEM OF THE GIANT SCALLOP. 22Q 



Very fine branches are given off from these vessels all along 

 their courses, which further divide to form systems of capillary 

 spaces that are finest and most numerous near the margins. 

 Some of these capillary spaces are large enough to be injected 

 with starch mass, and I have a preparation of the mantle lobe 

 from which only the infolded ridge has been removed, that was 

 dehydrated, cleared and mounted in balsam, in which the whole 

 system of vessels can be traced. A gelatin mass not only fills 

 the spaces mentioned, but passes out between the cells so that 

 in sections it may be seen to be diffused throughout the tissue. 

 This seems to hold good for all other parts of the body with the 

 exception of the gills, in which organs the mass is more com 

 pletely, but not entirely, confined to the blood spaces. The in- 

 dication therefore is, that the blood spaces are not confined ves- 

 sels, and that the blood functions as both blood and lymph. 

 The posterior pallial vessel may be traced far anteriorly, grad- 

 ually diminishing in size along its course. Here it finally joins 

 the anterior pallial vessel. The anterior pallial artery (Fig. 3, 

 apa) leaves the anterior aorta very near the cartilage and runs 

 directly to the anterior border of the hinge region of the mantle, 

 giving off vessels to this portion of the mantle on the way. 

 Here it branches into right and left vessels, each of which bends 

 abruptly ventrally (Fig. 5, apa] and pursues a course along the 

 anterior border of the mantle similar to that taken by the pos- 

 terior pallial artery at the other extremity of the animal. 



Along the anterior border of the mantle, near the dorsal line, 

 the vessel is rather small and slightly broken in its course. It 

 may be possible that this represents the border line between the 

 posterior and the anterior pallial arteries. There are other reasons 

 for believing that a large share of the animal is morphologically 

 equivalent to the posterior portions of other forms, and that the 

 anterior portion is greatly reduced. This has received attention 

 in another place. 



Several vessels leave the anterior aorta to supply the liver and 

 stomach. Most prominent among these is a vessel which leaves 

 the aorta between the points of origin of the anterior and posterior 

 pallial arteries. This bends out toward the left side of the liver, 

 where, in injected specimens, it is very conspicuous, passes ven- 



