55 



Laler the horizontal part of the distal wall and the rronlal wall of the zod'cium 

 separate from one another. While the distal half of the oa^cial bladder calcifies, 

 the proximal half continues to be membranous, and Vigelius thinks that the 

 egg passes along from the interior of the zoa>cium upwards towards the otrcium 

 between the distal wall and the frontal wall of the zooecium by which action 

 it i)ushes the membranous part of the ocecial bladder in front of it; he thinks 

 that this membranous part is later reabsorbed, which enables fertilisation of the 

 egg to take place through the aperture of the oa>ciuni. The portion of the frontal 

 wall of the zooecium, which is situated between the operculum and the free edge 

 of the ooecium, acts as operculum for the ooecium. This operculum is provided 

 with two muscular bundles, which reach from its free edge to the basal wall of 

 the zoa^cium and which by their contraction are able to draw it inwards. 



The present writer" in three papers, the last of which is a preliminary note 

 has given a series of investigations on the oa'cia and has shown there, that with 

 the exception of oa-cia, which are covered by kenozooecia, the oa»cia have 

 no such inner connection with the zooecium as Huxley, Nitsche, Hincks and 

 other writers have supposed. In all other cases therefore the egg must pass into 

 the ott'cium through the outer opening of this marsui)iuni. In the last paper 

 the author has set up eight different types of oa'cia, two of which (the epistomial 

 and the mesotoichal) in the present work are classed under the hyperstomial. 



In an important memoir chiefly dealing with the inner structure and with the 

 embryology of the Cheilostomatous Bryozoa Calvet" has examined the ooecia of 

 twenty one species belonging to the genera Biigula, Flustra, Membranipora, Micro- 

 porella. Chorb.npora, Schiznporella. Lepralia, Uiubonula, Retepora and (k'Hepora. With 

 the exception of ^Lepralid Pallasiana, in which he has found a membranous one- 

 layered marsupium formed by a basal evagination of the vestibulum and of 

 Cellarid fisliilosa he has found the oo-cium formed by two two-layered bladders, 

 a superior more or less calcified and an inferior membranous one, the last of 

 which is ])rovided with muscular strings destined for the opening of the ocecial 

 cavity during the setting free of the larvae. He has not been able to find any 

 coninuinication between the ooecium and the zocecial cavity and he therefore 

 thinks that the egg, to get into the oa>cium, must perforate the membranous 

 bladder. As to the ooecium of Cell, fistulosa he states that an opening exists in 

 the wall between the oa>cium and the zoctcium. 



In a very interesting paper Harmer^ has set forth the supposition, thai the 

 ooecia may be looked upon as formed by hollow spines and he founds this view 



54, p. 253. 55, p. 25 and 56, p. 11 — 18; ' !l. p. ^ 19, p. -283—284. 



