56 



especially on the structure and development of the ooecia in Algsidium parasiti- 

 cum and Euthyroides episcopalis. 



Before trying to give a division of the diffei-ent forms of ooecia, I must expres 

 my regret, that the material at my disposal has not allowed me to give a fuller 

 account of these formations, of which in many cases I have only been able to 

 examine the calcified portions. I hope, however, that my investigations will to a 

 certain degree facilitate the work of the investigators who may be able to com- 

 bine the desire to continue these studies with favourable conditions of procuring 

 suitable material. 



Endozooecial ooecia (PI. XXIV, figs. 6 — 11). 



We indicate by this name the ooecia which are immersed in the zooecia, gene- 

 rally, however, in such a way that they appear more or less distinctly on the 

 surface of these. Their main portion, the endoooecium, is formed by the zocecium's 

 distal wall, which in the free, frontal edge of the ooecium passes over into the 

 much less developed ectoocecium, together with which it forms a fold, the 

 ooecial fold. In the majority of cases the distal wall has a short horizontal 

 portion, provided with rosette-plates, which bends over into the helmet-shaped or 

 cup-shaped ooecium, and it is only in species of the genus Retiflustra (PI. XXII, 

 figs, b, 2 a), that the basal rim of the distal wall lies higher than the free frontal 

 edge of the ooecium. 



If we only pay attention to the calcified portions, we should think that these 

 ooecia were in internal connection with the proximal zooecium, but with the 

 exception of those ooecia, which are covered by kenozooecia, there seems really 

 always to be a membranous separating-wall between the zooecium and the 

 ooecium. 



We can divide these ooecia into two groups, according as the distal of the 

 two chambers, which bound the ooecium, is- an ordinary zooecium (autozooecium), 

 or a kenozooecium. We must also refer the ooecia, which are enclosed in the 

 avicularia, to this last-mentioned group. 



a) Endozooecial ooecia, which are enclosed in autozooecia. 



In the historical introduction we have referred to Vigelius' account of an 

 ooecium belonging to this type, namely, the ooecium in Flustra membranaceo- 

 truncata, and need only recall here that this ooecium, according to the description 

 of that author, is formed by a bladder-shaped infolding of the frontal membrane 

 of the zooecium meeting the distal wall. As our Museum does not possess colonies 

 of this species with developing ooecia, but on the other hand those of Flustra 

 securifrons, Ihe ooecia of which have essentially the same structure, we may test 

 the correctness of Vigelius' investigations by means of this species. The 



