272 Dr. J. Barrois on the 
2. On the other hand, there exists in the Escharina a less 
apparent organ of greatimportance. Situated directly beneath 
the pyriform organ, this organ consists of two small ridges 
formed by simple thickenings of the skin. In the larvee it 
easily escapes observation; and this explains why it has not 
hitherto been indicated. After fixation it is seen to increase 
to form a part of the adult organism; and it then becomes 
more easy to distinguish. 
Metamorphosis. 
In my memoir upon the metamorphosis of the Escharina I 
have already given a complete description of this, to which f 
may refer. I shall confine myself here to repeating the prin- 
cipal features. 
1. Fixation by the oral pole—The first phenomena of the 
metamorphosis consist in the devagination of the internal sac ; 
the sac comes forth and becomes converted into a square 
lamina, by means of which the fixation is effected. Are we 
to say that for this reason we must regard the sac as being 
only an adhesive organ belonging truly to the larval organ- 
ism? It would certainly be very rash to assert this; the 
function of securing the fixation may very well be performed 
by an organ originally destined to other uses and temporarily 
adapted to the function of a sucking-disk. In my opimion, 
the fact that I have just indicated proves nothing against the 
homology previously pointed out between the internal sac 
of the Escharine larve, the bilobate organ of the Entoproct 
larvee, and the cloacal sac of the adult form. 
However this may be, the oral surface is seen to smk down | 
upon itself after the issue of the sac, so as to form a small 
more or less shrivelled tube which unites the adhesive lamina 
to the edge of the circlet. 
2. Reversal of the mantle.—This fixation by the oral pole 
is accompanied, as in the Entoprocta, by a retreat of the ves- 
tibule into the interior of the embryo, but with a variation. 
which depends solely upon the difference in structure of the- 
larvee. 
In the Entoprocta the vestibule is fully formed, and its 
sinking into the interior of the embryo consequently does not 
necessitate any further change; but in the Escharina this is 
not the case. Here the aboral surface has lost the faculty of 
closing over the oral surface, and, further, the circlet has in- 
creased behind so as to surround the aboral surface with a 
kind of mantle, forming in this way a special cavity, playing 
the part of antagonist to the vestibule, and which I have 
called the pallial cavity. ; 
