Miscellaneous. 409 
Each of the two cesophageal rings emits branches to the Polian 
vesicles. 
If we examine carefully and with a low power the sand-canal of 
a Spherechinus for example, it is not difficult to recognize side by 
side with the sand-canal, which appears as a small whitish canal 
running along the ovoid gland to the madreporic plate, a second 
canal, closely applied to it, but distinguished from it by a darker 
colour, and which, at the level of the lower extremity of the 
gland, seems to widen a little and to become continuous with the 
tissue of the latter. On injecting this canal from the direction of 
the lantern, the material readily fills an cesophageal ring, passes 
into the Polian vesicles, and penetrates into the inner marginal 
vessel ; if the injection be made in the opposite direction, 7. ¢. from 
the direction of the gland, we may inject a rich network of small 
eapillaries which ramify on the surface of the latter. If by chance 
the gland be pricked with the canula, quite'a different result is 
obtained; the excretory canal which opens at the madreporic plate 
is injected, but never any vessels. 
From these facts it follows that the sand-canal is not a simple 
canal, but formed of two canals intimately united, one of which, 
the only one that has hitherto been described, is independent of the 
ovoid gland, while the other is connected with it. This result is 
confirmed by the study of transverse sections of the sand-canal, which 
show a first canal lined with a very regular epithelium, and, close 
beside it, a second canal, the lumen of which is partly filled up by 
some connective trabecule which start from the wall to forma 
delicate network bearing cells with a clear protoplasm, and fur- 
nished with processes and pigment-grains. By continuing the sec- 
tions as far as and including-the ovoid gland, the first canal is seen 
to retain always the same characters, and not to communicate with 
the gland ; on the other hand, the second canal, in proportion as it 
approaches the gland, increases in diameter; the partitions which 
divided its cavity become more numerous, and the elements that 
they support closer; the vessels which ramify on the surface of the 
organ become distinct, and, by continuing the sections, we arrive at 
the proper tissue of the gland, formed, like the homologous organ 
of the irregular Urchins, by very delicate connective trabecule 
bounding alveoli filled with cells, the protoplasm of which is fur- 
-nished with processes and granular nuclei, and more or less con- 
siderable aggregations of pigmentary masses. 
Tf, in a specimen already injected by the half of the sand-canal 
communcating with the excretory organ, we force in an injection 
through the ambulacral vessels, we shall fill, below the cesophageal 
ring lately mentioned, a second ring, which likewise sends forth 
branches to the Polian vesicles: it is from this second ring that 
starts the half of the sand-canal which is independent of the ovoid 
land. : 
: The communication between the two rings occurs at the level of 
the Polian vesicles; and in order that the liquid of one ring may 
pass into the other it must traverse the glandular tissue of those 
