Embryogeny of the Bryozoa. 393 
comparable to that with which we are acquainted in the other 
Ketoprocta. There is nothing in these phenomena which 
does not agree absolutely with what I have described in the 
marine species. 
To sum up, the larve of the freshwater Bryozoa are dis- 
tinguished only by three principal characters :—1, the absence 
of the ciliary circlet, which is replaced by a general ciliary © 
covering; 2, the absence of the endodermic mass; 3, the 
absence of the internal sac. ‘The first two characters are 
common to them and the larve of the Cyclostomata; the 
third is peculiar to them; nevertheless the Ctenostomata, in 
the group Chilostomata, present us with an analogous ex- 
ample of the reduction of the sac, a reduction which is very 
complete, if not total as in the Lophopoda. We see there- 
fore that the freshwater Bryozoa, in their development, do 
not present any important phenomenon with which the inves- 
tigation of the marine types has not already made us familiar. 
We may remark in passing that the great resemblances of 
the larvee of Lophopoda and Ctenostomata to those of the 
Cyclostomata and Chilostomata seem to justify a distribu- 
tion of the Ectoprocta into two great divisions :—1. Cyclo- 
stomata-Lophopoda; 2. Chilostomata-Ctenostomata. 
Conclusions. 
Characters of the larva.—Filiation of the larve.—Leaving 
out of consideration the accessory organs, we may endeavour 
to give a purely diagrammatic representation of the principal 
larval types, by bringing together their essential parts, which 
the detailed study of the metamorphosis has shown us to be of 
the most importance. We shall then find that a Bryozoan 
larva consists essentially of five principal parts :— 
1. The aboral surface, or the integument of the cell (A). 
2. The peripheral part (O) of the oral surface, with the 
circlet which is formed by its margin, destined to form the 
mass of globules which fills the young cell, and, no doubt, 
originally the connective reticulum of the general cavity. 
3. The incubatory pouch (1) with the central part of the 
oral surface destined to form the intratentacular space. 
4, The intestine (2). — 
5. The rudiment of the polypide (3), a portion which is 
already preexistent in the larve, in which it very generally 
forms a special organ called the hood, and takes a variable 
part in the formation of the polypide, sometimes forming only 
the aperture of the cell (Emtoprocta), sometimes constituting 
almost the whole polypide. 
1, Entoprocra.—Figure 1 (Pl. XIV.) represents the ar- 
