Messrs. Hancock and Embleton on the Anatomy of 101 
on account of the great difficulty of injecting such small animals, 
and from a feeling of the unsatisfactory nature of such an ope- 
ration on tubes so delicate as the minute branches we have ob- 
served. The existence however of intervisceral lacunae we do not 
wish to deny, since the valuable papers of M. Milne Edwards in 
the ^ Annales des Sciences Naturelles^ seem to establish the fact 
of their presence in nearly the whole of the Mollusca. 
The branches of veins coming from the skin, represented in 
PI. IV. fig. 2 ssss, have been several times verified ; from four 
to six venous branches have been made out, uniting so as to form 
two large trunk-veins, fig. 2ppp' p' and fig. 4;eedd, on each 
side, which joining together pour their united contents at once 
into the auricle : one of these veins can be seen along the inner 
aspect of the skin as far forwards as opposite to the transverse 
portion of the intestine, receiving branches, fig. 4< g g y y, in its 
course from the skin, into which its most advanced branch pene- 
trates ; the other and much smaller vein turns backwards, and 
enters the skin sooner than the former, after visibly receiving a 
small branch or two from it. Entering the posterior part of the 
auricle is the posterior trunk-vein, fig. 2 q and fig. 4 d, which 
coming from the back part of the skin receives three pairs of 
branches at least : one pair appeared coming from below as if 
from the ovary, but was not so distinctly made out as the rest. 
If we attempt to trace the veins into the skin, we find that they 
communicate with a system of sinuses therein. This network of 
sinuses pervades the whole of the skin, being abundant on the 
sides under the bases of the papillae, and on the foot, and we 
suppose communicates freely with the system of intervisceral 
lacunae pointed out by Milne Edwards. Whether the lacunae of 
the skin have any thing like a symmetrical arrangement as prin- 
cipal trunks or canals, we have not been able to determine ; but 
if a cross section of a papilla be made, a distinct canal becomes 
visible at each extremity of the section, as shown in fig. 6 c c, 
and from this and the symmetrical order of the venous trunks 
passing from the skin to the auricle, we might infer that such an 
arrangement exists. Those canals run the whole length of the 
papilla, and communicate with the meshes of a delicate cellular 
tissue which lines the skin of that organ ; at the base of the papilla, 
they open into the sinuses of the skin. The position of these 
canals in the papillae, and the cellular tissue in connexion with 
them, are indicated in PI. IV. fig. 9 of our former paper on the 
digestive system. 
The general course of the blood will be necessarily then from 
the ventricle along the arteries to the viscera and to the skin ; 
in the first case it passes from the arteries, in a way we do not 
understand, into the lacunae among the viscera and between them 
