408 Miscellaneous. 
the polypides of the sexual zocecia. At the time of reproduction 
the ova detaching themselves successively from the ovary float in 
the perivisceral cavity; they then show irregular shrivelled forms 
and are furnished with a very delicate transparent shell. In this 
state they pass one at a time through the intertentacular organ of 
the expanded polypide, and when they thus get into the water they 
become regularly ovoid and the contents regularly spherical. 
During this process, which may last for some days, the sperma- 
tozoids press round the ovary and the ova detached from it. The 
author could not determine the precise moment of fecundation, but 
thinks that it takes place before the formation of the shell. Under 
any circumstances the intertentacular organ here fulfils the functions 
of an oviduct and the development is external. 
The reproduction of A. duplex is more complex and very interesting. 
At the moment when the sexual elements are about to be developed 
the zocecium is occupied by a polypide destitute of any intertentacular 
organ, and a cellular mass destined to form the spermatozoids 
appears against the wall of the stomachal cecum. At the same 
time towards the aboral extremity of the same zocecium a second 
polypide is formed, upon the funiculus of which young ovules origi- 
nate. Thus one zocecium has two polypides of different ages, of 
which the older one may be called the male and the other the female 
polypide. The male polypide soon begins to degenerate, leaving in 
the cell the brown body and a mass of spermatoblasts, while the 
female polypide, which continues growing, takes its place. The 
zocecium then contains only a single polypide, the female, and this is 
furnished with an intertentacular organ. Later on the ova are seen 
to have passed into the sheath of this polypide probably by means 
of the intertentacular organ ; they have a transparent shell and are 
attached, to the number of seven or eight, by a fine peduncle to the 
walls of the sheath, where their development takes place. 
The liberation of the larve is very simple. When the polypide 
proceeds to expand the ovigerous part of the sheath becomes evagi- 
nated, forming a papilla, to the apex of which the ova are appended, 
and the larvze which have completed their development burst through 
the shell and escape into the water. Thus in A. duplex two poly- 
pides of different sexes at first coexist in the same zocecium ; then 
the female polypide takes the place of the male and alone possesses 
the intertentacular organ through which the ova are evacuated ; but 
while in A. albidum the ova are passed by this organ into the 
external medium, where they undergo a free development, in A. 
duplex it only conducts the ova into the invaginated sheath when 
their development takes place as in a sort of marsupium. 
In Pherusa tubulosa, the polypides of which have no intertentacular 
organ, the larval form is a bivalve larva nearly identical in struc- 
ture with that of Flustrella. The only known Bryozoan larvee with 
two chitinous valves were those of Membranipora (Cyphcnautes) and 
Flustrella ; Pherusa furnishes a third example of this larval form.— 
Comptes Rendus, July 29, 1889, p. 197. 
