276 Dr. J. Barrois on the 
rudiment of the future polypide. It is here that I have seen 
most distinctly the superposition of the cells of the skin upon 
the circle formed by the radiating cells: the fact appears here 
so clearly as to cut short every doubt; and it is for this reason 
that I point it out. : 
3. Of the second stage of the metamorphosis.—The deve- 
lopment appears to depart more from the type of the Escha- 
rina in the second stage of the metamorphosis at the period 
when the adhesive plate (composed of its two superposed in- 
flations) becomes united with the skin of the aboral surface, 
to give origin to a club-shaped stage. We then see the whole 
of the hood sink into the interior in a very sudden fashion, 
and not gradually, as in the case of the Escharina ; moreover 
it penetrates much more deeply than was seen in the prece- 
ding group. Before stopping, and even before reaching the’ 
opaque ring formed by the circlet, it traverses this ring, so 
that the rudiment of the polypide is soon situated beneath the 
ciliary cirelet. Unfortunately I have not yet studied the 
changes which take place in the rudiment of the polypide 
during this passage across the ring formed by the cells of the 
circlet ; it is probably at this moment that the phenomena 
take place which correspond to the meeting of the two rudi- 
ments which we have indicated in the Escharina. 
It is not long after this club-shaped stage, in which the 
rudiment of the polypide is seen placed beneath the circlet and 
in the posterior part, that the cell begins to swell, to give 
origin to the stage described by authors. Here we fall in 
with known phenomena. 
- [V. Crenostomata. (Pl. XIV. figs. 3 and 8.) 
In -the Ctenostomata, and especially in the species that I 
have taken as the type (Sertalaria lendigera), the increase of 
the cells of the circlet is carried to the extreme point, and with 
it all the consequences which foliow upon it. The cells of 
the circlet form ribs of great length, which occupy almost the 
whole surface of the larva; the oral surface is almost entirely 
enclosed ; one of the two poles is occupied by an exceedingly 
reduced small hood, the other by a free portion of the oral 
surface reduced to quite rudimentary dimensions. Lastly, 
and this is especially the great fact characteristic of the larvee of 
Ctenostomata, the internal sac is nearly atrophied; it no 
longer possesses an internal cavity, and is reduced to a small 
solid mass adherent to the inner surface of the residue of the 
oral surface. 
