55 



Later the horizontal part of the distal wall and the frontal wall of the zooecium 

 separate from one another. While the distal half of the ocecial bladder calcifies, 

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

 egg passes along from the interior of the zooecium upwards towards the ooecium 

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

 it pushes 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 ooecium. 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 zooecium 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 ocecia and has shown there, that with 

 the exception of ocecia, which are covered by kenozooecia, the ocecia 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 ooecium through the outer opening of this marsupium. In the last paper 

 the author has set up eight different types of ocecia, 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 ocecia of 

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

 porella, Chorizopora, Schizoporella, Lepralia, Umbonula, Retepora and Cellepora. With 

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

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

 Cellaria fistulosa he has found the ooecium formed by two two-layered bladders, 

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

 which is provided 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 

 communication between the ooecium and the zooecial cavity and he therefore 

 thinks that the egg, to get into the ooecium, must perforate the membranous 

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

 the wall between the ooecium and the zooecium. 



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

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



1 54, p. 253. 55, p. 25 and 56, p. 11—18; M, p. ' 19, p. 283—284. 



