Miscellaneous. 451 
On the Circulatory System of Spatangus purpureus, 
By M. R. Kanuer. 
The buccal aperture of Spatangus purpureus is surrounded by 
two vascular rings—an outer one, belonging to the blood-vascular 
system, and an inner one, belonging to the ambulacral system. The 
same arrangement recurs in the ambulacra. 
Hoffmann’s branch of communication, which connects the intestinal 
vessel with the only peribuccal ring described by that author, really 
divides at the level of the mouth into two branches, one of which 
opens into the sanguiferous ring, and the other into the ambulacral 
ring. 
In the same way the sand-canal is double in that part of it in- 
cluded between the opening of the mouth and the extremity of the 
cesophagus ; it is formed of two canals placed close together, each of 
which opens into the corresponding peribuccal ring. At the level 
of the extremity of the cesophagus (first curvature) these two canals 
unite in one, which continues simple as far as the point where the 
second convolution of the digestive tube joins the third. Beyond 
this region it becomes partitioned off again into several secondary 
cavities, four or five in number, at the moment of its arrival at the ~ 
organ commonly called the heart, in which it loses itself. It 
becomes reconstructed after having traversed this organ, and reaches 
the madreporic plate in the form of a slender canal of peculiar 
structure. 
The supposed heart is a spongy organ, the interstices of which be- 
come completely filled when the sand-canal is injected. It is composed 
of connective tissue supporting numerous nuclei and elements like 
those of the blood and of the general cavity. Are we to regard this 
organ as a sort of blood-vascular gland ? or simply as an organ of 
secretion? The so-called membrane which surrounds the extremity 
of the sand-canal and unites it with the madreporic plate also ap- 
pears rather to be a gland in connexion with that canal. It pre- 
sents a structure analogous to that of the heart. 
The digestive tube receives the blood from the inner and outer 
marginal vessels. It only possesses vessels in the region included 
between the first orifice of the siphon and the origin of the third 
convolution ; the cesophagus, the third convolution, and the rectum 
do not receive a singleone. Moreover, where the vessels exist, their 
distribution is far from being so regular as figured by Hoffmann. 
The ventral surface of the second convolution receives no vessel, 
except in the neighbourhood of the orifice of the diverticulum and 
on each side of that organ ; it is the dorsal surface that receives the 
greater part of the vessels. The intestinal vessel of Hoffmann, 
which, according to him, furnishes vessels to the stomach, the third 
convolution, and the rectum, really dies out a little beyond the 
origin of the branch of communication without reaching the sto- 
mach, the vessels of which present the following arrangement :— 
The two marginal vessels of the second convolution form a very close 
plexus around the orifice of the diverticulum ; and from this originate 
