Miscellaneous. 85 
as the heart, to which the vertical canal is intimately united, but 
without having any relations to it except those of contiguity. The 
organ in question és therefore not a heart, as has hitherto been believed ; 
and we shall recur immediately to its structure. Having arrived at 
the point where the esophagus penetrates into the lantern, the vertical 
vessel opens into a circular vessel resting on the superior membra- 
nous floor of the lantern and bearing opposite to each of the pyramids 
a small racemiform gland (Poli’s glands). This, whatever may have 
been said, is the only vascular ring presented by the circulatory ap- 
paratus of the Echinida ; at least I have found it impossible to discover 
any other. From this ring, opposite to the intervals of the pyramids 
and consequently alternating with Poli’s glands, spring five radiating 
vessels which pass beneath the calcareous piece known as the- falx, 
and become widened so as to ocewpy the whole width of the inferior 
surface of this piece. Arriving at the outer margin of the lantern 
these radiating canals resume their original calibre and run along 
the outer surface of the lantern, from which, however, they finally 
separate, so that each of them may become continuous with one of 
the five ambulacral canals. The latter are produced a little towards 
the mouth beyond their point of junction with the five vertical canals; 
it is this, no doubt, that has led to the belief in the existence of a vas- 
cularring applied tothe buccal membrane within the lantern; but this 
ring has no existence: the prolongations of the ambulacral canals 
soon bifurcate ; and each of their branches penetrates into one of the 
two large buceal tentacles. 
The ambulacral canals ascend along the test, and terminate cecally 
below the pore presented by the so-called ocular plates, although 
these do not contain any organ of vision. In Echinus sphera this 
pore is closed by a continuous membrane, and does not give passage 
to any thing resembling an unpaired tentacle. Although one can 
inject the whole circulatory apparatus by applying to one of these 
pores the pipe of a syringe, there is not in it any direct communi- 
cation between the vascular apparatus and the exterior; the injec- 
tion only penetrates in consequence of a lesion. ‘There is no anal 
ring uniting the five ambulacral vessels. Each canal is the seut of 
a double current maintained by the vibratile cilia which clothe its 
interior ; it serves at once for the flow and the return of the san- 
guine liquid which it contains, as I have been able to ascertain by 
direct observation. The arrangement of the ambulacral vessels of 
the Echinida therefore exactly reproduces that which I have already 
described in the Comatule. 
Immediately opposite to the right upper Poli’s gland there springs 
from the circular vessel of the lantern a vascular branch which 
ascends along the cesophagus, and forms, to a certain extent, a pen- 
dant to the vertical canal which originates from the madreporie 
plate and opens at the left posterior Poli’s gland. Having reached 
the point where the cesophagus opens into the intestine, this canal 
becomes reflexed and considerably widened, and constitutes the great 
vessel which follows the inner margin of the intestine, and beyond 
which the mesenteric plate is slightly prolonged. There is con- 
