274 Dr. J. Barrois on the 
logous with the labial thickening of the Entoprocta. There 
is consequently a complete correspondence in all points. 
Thus in the Entoprocta, as in the Ectoprocta, the polypide 
may be regarded as originating from the amalgamation of two 
distinct rudiments coming, one from the aboral surface of the 
larva, the other from the upper part of the vestibule of the 
larva, and which unite to form the polypide. In the Ento- 
procta the former (the labial thickening) is small, and gives 
origin only to the aperture of the cell, and the second, con- 
taining the entirely developed digestive tube, gives origin to 
nearly the whole of the polypide. In the Hectoprocta the 
reverse is the case: the former (the hood) is the more im- 
portant, and it is this that forms nearly the whole of the 
polypide ; the second is comparatively restricted, and gives 
origin only to the muscular connective parts of the future 
polypide. There is nothing very surprising in this variable 
intrusion of the two rudiments into one another; we have in 
the same way in the Tunicata an important portion, the 
cloacal tubes, placed at the boundary of the endoderm and ecto- 
derm, and furnished sometimes by the one, sometimes by the 
other of those layers. 
Lepralia Pallasiana.—In order to judge of the degree of 
constancy of the phenomena described in Lepralia unicornis, 
it will not be without interest to examine a second species of the 
same family before passing to other groups. The following 
are the results which I have obtained by the careful study of 
Lepralia Pallasiana, a species of the same family, but of a 
type very distinct from that of L. unicorns. 
The sole differences that we could observe only commence 
at the close of the metamorphosis, at the moment when the 
skin removes from the internal organs to give rise to the square 
stage. We observe that in Lepralia Pallasiana the fatty 
mass, instead of retaining the horseshoe-shape more or less 
resembling that of the circlet, forms a square lamina, 
which surrounds the rudiment of the polypide. Moreover 
this rudiment, when once formed, does not separate again from 
the aggregation of globules with which it is in contact by its 
posterior part. 
In Lepralia unicornis we have three stages :— 
1. The two rudiments of the polypide unite so as to form 
a continuous cord from the aperture of the cell to the fatty 
mass. 
2. They become concentrated into a small mass suspended 
from the skin. 
3. The rudiment, definitively formed, has again become 
elongated as far as the fatty mass. 
