MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 139 



The discovery of the pallial arterial system is due to Willey, who by meaus of injections 

 was enabled to describe this peculiar system. The lesser aorta divides into two branches almost 

 immediately aftei- leaving the heart. One branch, the septal, goes backward and supplies blood 

 to the siphuucle and the septal region of the body wall. The other branch, the pallial artery, 

 bends downward to the middle line of the body wall and then runs straight forward below the 

 skin on the surface of the renal sacs, and then in the median line of the ventral portion of 

 the mantle nearly to its anterior edge. From its posterior part the pallial artery gives off 

 branches to the intestine and the rectum. In front of the anus, at the posterior Umit of the thin 

 portion of the mantle, it gives off a large branch upon each side, the branchio-osphradial arteries. 

 These supply the posterior portion of the mantle and '"send up branches to the tips of the 

 branchiae, supplying the integument of the latter, and also a small branch into each of the 

 osphradia. ... In the female they also supply the nidamental gland." As the pallial artery 

 passes foi-ward it gives off several small branches to the lateral portions of the mantle. Arriving 

 near the edge of the mantle it divides into two branches, which turn to either side and follow 

 the posterior edge of the muscular margin of the mantle, the marginal pallial arteries. Very 

 numerous and regularly arranged short branches, the radial pallial arteries, spring from the ante- 

 rior side of the marginal pallial arteries, while longer and more irregular liranches pass from 

 the marginal pallial arteries backward into the middle parts of the mantle. 



The marginal pallial arteries do not finally end in capillaries or blood sinuses, but unite with 

 the pallio-nuchal branches of the dorsal aorta, thus forming a complete arterial circle, discovered 

 by WiLLET, which he has named the circulus pallialis. The union takes place at the dorsal sides 

 of the shell muscles. 



In addition to forming a union with the marginal pallial arteries, the pallio-nuchal arteries 

 give off' branches to the dorsal portion of the mantle, and to the dorsal nuchal region of the body 

 wall (the region which is hollowed out to receive the involution of the shell), and to the crura of 

 the funnel. 



In regard to the pallial veins Wflley says the following: 



"When a Nautilus becomes moribund it usually rises to the surface, owing to an abundant 

 production of gas in the interior of the body. If it is allowed to die and is then removed from 

 the shell the veins are found to be injected with gas of some sort, and the finest ramifications of 

 the veins, in the mantle at least, are displayed with a clearness which could hardly l)e attained by 

 artificial injection. 



"The mantle is simply riddled by these veins in a manner which defies one's powers of 

 draftmanship. The veins are collected into two main trunks, which lie on either side of the 

 anterior pallial artery, and proceed backward to open into the afferent branchial vessels. At the 

 sides of the mantle there are also a number of lateral pallial veins, which open into a large sinus 

 situated over the shell muscles." 



The mantle of the specimen Owen described possessed a peculiar abnormality. Its opposite 

 sides had grown together a)»ove the funnel so that Owen describes and figures it as "perforated 

 by a large aperture through which the funnel passes." 



BODY WALL. 



The inner side of the mantle cavity is formed by the body wall, to which I wish to devote 

 a few words so as to la}' a foundation for a point to be brought forward later. 



Laterally — i. e. , at the sides of the body — the inner waU of the mantle cavity is formed by the 

 sides of the great shell muscles alone (Figs. 3 and -i). These muscles pass from the cephalic 

 cartilage outward and backward, forming the sides and part of the floor of the middle region of 

 the body wall, to be attached one to each side of the shell just anterior to the edge of the last 

 septum. Perhaps we might say that they end immediately back of the lateral portions of the 

 mantle cavity, for these parts of the mantle cavity are lunited posteriorly bj- the outer ends of 

 the shell muscles. The muscles are only about 5 centimeters in length, but 2.5 centimeters in 

 breadth by 1.75 centimeters in thickness. These dimensions convey an idea of what the power 



