Embryogeny of the Bryozoa. 275 
In Lepralia Pallasiana (and, I believe, in a good many 
other species) we pass directly from stage 1 to stage 3. 
Such are the kinds of variations that we discover between 
the different types, when we do not go beyond the group 
Escharina. We will now pass to the more distant groups. 
Ill. Ceniunarina (Bugula avicularia). 
Larva. 
The larvee of the Cellularina belong to the same type as 
the larve of the Kscharina; but in some species, such as 
Bugula avicularia, they differ therefrom by a greater elonga- 
tion of the cells of the circlet. This elongation causes the 
free portion of the oral surface to be reduced to a degree of 
which we find no example among the Hscharina; while the 
enclosed portion has acquired an extraordinary length, and 
occupies nearly the whole height of the young larva. 
Moreover the skin of the larva, which in the Escharina may 
be regarded as composed half and half of each of the two 
surfaces (oral and aboral), is here formed chiefly by the circlet. 
Metamorphosis. 
Nevertheless the length of the cells of the circlet has not 
here any influence upon the metamorphosis, which takes place 
absolutely, as in the Escharina, by direct reversal ot the 
mantle; it is necessary, however, to note particularly the 
peculiar form of the adhesive lamina and the aspect of the 
hood after fixation. 
1. Adhesive lamina.—The adhesive lamina has no longer 
the same form that I have described in the Escharina. In 
the latter the internal sac of the larva contained two small 
symmetrical elevations, which, after fixation, only made more 
distinct the angles of the kind of lozenge formed at this period 
by the adhesive lamina; in the Bugule these two symmetrical 
elevations are replaced by asingle more voluminous elevation 
which fills nearly the whole cavity ot the sac. Atter fixation 
this elevation torms a large mamilla at the bottom of the 
adhesive lamina, causing the latter to appear double, and 
formed of two superposed inflations, of which the inferior and 
smaller one originates from the interior projection of the sac, 
and the larger superior one from its wall. 
2. Hood.—The hood, coloured by means of carmine, shows 
us, principally after fixation and very distinctly, its essential 
part composed of a circle of radiating cells situated beneath 
the skin of the aboral surface, and which I regard as the first 
