56 



especially on the structure and development of the ooecia in Aliisuliiiin jxirasili- 

 ciim and Euthiiroides episcopalis. 



Before trying to give a division of the dilTerent forms of orrcia, I must ex[)res 

 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 hoj)e, liowever, 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 witli favourable conditions of procuring 

 suitable material. 



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



We indicate by this name the ort'cia which are immersed in the zon^cia, 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 zoffcium's 

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

 much less developed ectooa'cium, together with which it forms a fold, the 

 od'cial 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. 1), 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 willi the proximal zoa'cium, but with the 

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

 always to be a mendiranous separaling-wall between the zoo'cium and the 

 ott'cium. 



We can divide these oa'cia into lw(3 groups, according as the distal oi' the 

 two chambers, which bound the oo'cium, is an ordinary zocecium (autozooecium), 

 or a kenozoa'cium. Wc must also refer the oo'cia, 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 Vi gel ins' account of an 

 oa^cium belonging to this type, namely, the ocrcium in Fliistra membranaceo- 

 tnincald, and need only recall here that Ibis oo'cium, according to the description 

 of that author, is formed by a bhulder-sliaped infolding of the IVontal membrane 

 of the zoo'cium meeting the distal wall. As our Museum does not possess colonics 

 of Ibis species with developing ooecia, but on llie other hand those of Fliistra 

 seciirifrons, Ihe oa'cia of which have essentially the same structure, we may te.st 

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



