270 Dr. J. Barrois on the 
them a portion of the skin, so as to give origin to a circular 
fold formed by the cells of the circlet lined by a portion of the 
aboral surface. This fold forms a true mantle, which in- 
creases above the aboral surface, and finally covers it more or 
less completely. 
This envelopment of the aboral surface by a mantle gives 
rise to the formation of a pallial cavity. In the Escharina 
the envelopment is never complete, and the extremity of the 
aboral surface, occupied by a special organ called the hood, 
always continues to project beyond this cavity. This hood, 
formed principally by a circle of radiating cells placed beneath 
the skin, is, in my opinion, by no means the homologue of 
the caudal appendage of the larve of the Hntoprocta, but 
of the labial thickening which appears in the latter after 
fixation. 
Towards the oral pole there is no elevation, and the sole 
effect of the elongation of the cells of the circlet is to reduce 
more and more the space at first occupied by the oral surface, 
which becomes depressed and becomes thinner in proportion. 
It is at first upon the anterior portion, furnished with the 
pyriform organ, that the whole reduction exclusively takes 
effect ; it becomes slender, depressed, and thinner, and finally 
reduced to an elongated fissure edged on each side by the 
cells of the circlet. 
Thus the oral surface is early divided into two distinct 
portions—a free portion of rounded form, and a narrow por- 
tion enclosed in the circlet. ‘The former always coincides with 
the oral pole: it becomes reduced without interruption, to the 
profit of the second, in proportion as the encroachment of the 
circlet progresses ; but in the Escharina it is still tolerably 
wide. 
2. Endoderm.—The endoderm originating from the gastrula 
does not, as in the Entoprocta, give origin to a complete and 
well-formed digestive tube, but soon resolves itself into a 
compact mass of not very distinct elements—the vitelline 
mass, Which for a long time occupies the interior of the em- 
bryo; in the larva we find it broken up into disseminated 
globules. We may regard the vitelline mass as representing 
the digestive tube, which is deficient in the larvee of Hn- 
toprocta. 
In a single species investigated by Repiachoff, the endoderm 
of the gastrula (formed, however, in the same maniner as in 
the other larve of the group Kctoprocta) is seen to give 
origin to a complete digestive tube. ‘This fact certainly pos- 
sesses much interest, and places beyond dispute the homology 
that I have just indicated between the digestive tube of the 
