53 



Nevertheless we can only understand his view of the structure of the ooecium, 

 and of the relation of the eggs to it, after reading Nitsche's later but fuller 

 description of the ooecium in Bicellaria ciliata, which is built in a similar way. 



Busk* introduces the name i>ovicells«, which is still used by some writers, 

 for the here discussed formations, but the older view of them as capsules, con- 

 taining the ovaries, was first altered by Huxley's^: »Note on the reproductory 

 organs of the Cheilostome Polyzoa.- He proposes here the now prevailing view 

 of the ooecium as marsupial chambers, into which the eggs are brought from 

 the zooecium to develop into larvae. He found namely in Bugula avicularia, that 

 the egg is formed in the zooecium where it is attached to the funiculus near the 

 stomach and also that the originally empty ooecium at a certain time was seen 

 to contain an egg, which was more developed than the one observed on the funi- 

 culus, and which after cleavage became an embryo provided with cilia. 



Against Huxley's view Hincks^ maintains, that the eggs from which the 

 ciliated embryos are developed according to his investigations are formed in the 

 ooecia (ovicells) of a shapeless, grained mass. As to the eggs which Huxley found 

 in the zocecia Hi neks states that they are most common in zocecia, the ooecia 

 of which have emptied their contents, and they can even be found in zocecia, 

 the polypide of which are dead, from which it must be concluded that they are 

 only set free on the dissolution of the soft content of the zooecium. They are 

 never ciliated at any stage of their development. 



The first detailed account of an ooecium is given by Nitsche*, who describes 

 the development and structure of the ooecia in Bicellaria ciliata. He represents it 

 as formed of two hollow, two-layered, bladder-shaped outgrowths from the margin 

 of the zooecium; the smaller, which is membranous, is grown over by the larger, 

 the outer wall of which is calcified, and which in the full-grown condition forms 

 a helmet-shaped body connected by a short stalked portion with the zooecium. 

 The membranous bladder serves as an operculum for the helmet-shaped portion, 

 and its interior is penetrated by a muscular chord, by the contraction of which 

 its rim withdraws from the edge of the ooecium so that the larvae can get out. 

 In the above-mentioned work of Re id attention had already been called to the 

 fact that this membranous operculum of the ooecia in Bagula avicularia, which 

 contains larvae, undergoes rhythmical contractions (»This membrane was observed 

 in a few instances where the ova were fully formed to contract and relax at 

 intervals, and in this way it may assist in the escape of the ovum«. Without 

 knowing Huxley's observations Nitsche arrived at the same result with regard 



1 3; " 39; ' 37; ' 79. 



