408 Miscellaneous, 



the polypides of the sexual zooecia. 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 ^. duplex is more complex and very interesting. 

 At the moment when the sexual elements are about to be developed 

 the zooecium is occupied by a polypide destitute of any intertentacidar 

 organ, and a cellular mass destined to form the spermatozoids 

 appears against the wall of the stomachal ca)cum. At the same 

 time towards the aboral extremity of the same zooecium a second 

 polypide is formed, upon the funiculus of which young ovules origi- 

 nate. Thus one zooecium has two polypides of different ages, of 

 which the older one may be caUed the mcdeandi the other the/emaZe 

 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 

 zooecium then contains only a single polypide, the female, and this is 

 furnished ivith an intertentacidar 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 larvee 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 larva3 which have completed their development burst through 

 the shell and escape into the water. Thus in A. dupdex two poly- 

 pides of different sexes at first coexist in the same zooecium ; then 

 the female polypide takes the place of the male and alone possesses 

 the intertentacular oi'gan through which the ova are evacuated ; but 

 while in A. alhidmn the ova are passed by this organ into the 

 external medium, where they undergo a free development, in A. 

 diiplex it only conducts the ova into the invagiuated sheath when 

 their development takes place as in a sort of marsupium. 



In Pherusa ttdndosa, the polypides of which have no intertentacular 

 organ, the larval form is a bivalve larva hearly identical in struc- 

 ture with that of Fhistrella. The only known Bryozoau larvse with 

 two chitinous valves were those of Memhranipjora (Cgp)hi,7i':mtes) and 

 Flustrella ; Pherusa furnishes a third example of this larval form. — 

 Comptes liendus, July 29, 1889, p. 197. 



