150 ARTHUR WILLEY. 
artery, since among their minor ramifications they send up 
branches to the tips of the branchiz supplying the integument 
of the latter, and also a small branch into each of the osphradia 
(i.e. into the osphradia of Lankester and Bourne, and into 
those which I described in my last letter). In the female they 
also supply the nidamental gland. 
The posterior pallial artery runs backwards over the ventral 
surface of the heart, leaves the pericardium through the orifice 
described by Owen, and then passes onwards below the skin to 
the left of the genital gland, between the latter and the gizzard. 
Upon reaching approximately the middle point of the posterior 
rounded surface of the body it, too, passes into the integument, 
and immediately divides into two main branches, right and 
left, which supply the dorsal and posterior regions of the 
mantle, including the siphuncular pedicle. A variable number 
of small secondary or tertiary branches go up into the siphun- 
cular pedicle, but there is one branch which is essentially the 
siphuncular artery (see Figs. 2 and 3). But even the definite 
siphuncular artery is not constant in its origin, but arises now 
from the right and now from the left of the two main branches 
of the posterior pallial artery. The siphuncular artery is 
therefore a minor ramification of the posterior pallial artery. 
Owen, followed by Vrolik, described the latter as passing 
in toto into the siphuncle. Keferstein, whose figure is more 
accurate in this respect, says that it passes ‘‘ nach hinten zur 
Korperhaut und besonders zum Sipho.” 
Injection indicates that the arteries which supply the 
siphuncle are homodynamous with the other ramifications of 
the posterior pallial artery. 
5. Pallial Veins.—It is not now necessary to go into de- 
tails with regard to the pallial veins, but I will point out how 
they may be seen to great advantage. 
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 
