398 Dr. J. Barrois on the 
We then see that the oral surface, entirely invaginated into 
the interior of the embryo, divides into two completely different 
parts, one of which remains adherent to the base of the cell, 
while the second advances upwards to connect itself with the 
special invagination of the aboral surface (invagination of 
the hood in the Ectoprocta, labial thickening in the Ento- 
procta), and constitute with it the future polypide. 
In the Entoprocta this second part, or superior division of 
the vestibule, is greatly developed, and consists of the median 
portion of the oral surface, which bears the incubatory pouch, 
and to which the intestine is suspended; it forms of itself 
almost the entire polypide, while the invagination of the aboral 
surface hardly gives origin to more than the aperture of the ~ 
cell. In the Ectoprocta it is otherwise: the upper part of 
the wall of the vestibule only consists of a small cellular mass 
which comes to surround the principal portion of the polypide, 
of which it will form no more than the musculo-connective 
appendages ; the essential part or epithelial lamella of the 
future polypide is here furnished entirely by the invagination 
of the aboral surface. 
To sum up, we see that in both cases the polypide is formed - 
by the union of two rudiments of very distinct origin; these 
rudiments encroach upon each other in such a manner that 
sometimes one, sometimes the other, plays the essential part 
in the formation of the polypide. This proves nothing 
against the general concordance which otherwise exists in 
the general phenomena. We have already noticed that in 
the Ascidia we see in the same way one of the most impor- 
tant portions, the cloacal sac, situated between the two primi- 
tive lamellae, and formed sometimes by one, sometimes by 
the other of these lamelle. It must further be noted that, in 
- the Ectoprocta, the great development of the invagination of 
the hood, and the predominant part which it takes in the 
formation of the polypide, also depend certainly in great part 
upon the degenerescence of the intestine, which is itself the 
sequel of the larval state. In most types, moreover, we see 
the mass of globules which represents the digestive tube of 
the larva join itself onto the cecal extremity of the polypide, 
so as likewise to take part in its formation. 
The lower portion of the vestibule, including the circlet 
which forms part of it, enters into degenerescence in both 
types, so as to form the thick mass of globules which plays 
such an important part in the embryogeny of the Chilosto- 
mata. It would appear nevertheless, as is especially notice- 
able in the Entoprocta, that the primary function of this 
lower part is to give origin to a connective reticulum, which 
