60 



The endoocecium, as in the foregoing group, is formed by the distal wall be- 

 tween two chambers lying in the same longitudinal row, but while the ecto- 

 ocEcium in that group was only represented by a more or less distinctly limited 

 part of the frontal membrane of the covering zooecium, it is here so to speak 

 represented by the whole covering chamber, which is a kenozooecium. We find 

 everywhere a common operculum for the kenozooecium and the ooecium. Such 

 ooecia are found in Didymia simplex (PI. IV, fig. 7 d), Eucratea chelata, Bicellaria 

 infundibulata (PI. IV, figs. 4 a -4 d), Menipea crijstallina (PI. IV, figs. 1 a, 1 b), 

 Cribrilina punctata (PL IX, fig. 11 h), Cr. annulata, Cr. Gattijae (PL IX, fig. 12 a), 

 Escharella dinphana (PL XVII, fig. 1 a), Esch. abyssicola (PL XVII. fig. 2 a), 

 Eurystomella foraminigera (PL XVIII, figs. 14 a— 14 b), E. bilabiata, besides in the 

 Farciminaria species (PL I, figs. 10 a— 10 c), most members of the family Catena- 

 riidae (Pis. XI, XII, XIII, XV), and the members of the family Hippothoidae 

 (PL XXI, figs. 8e, 8 b, 9 a, 9 c). 



The fact that the endoooecial ooecia, besides appearing as a rule in certain 

 families, appear sporadically in more or fewer forms in a number of other 

 families would seem to suggest that they represent an old ooecial type, which 

 perhaps was at some time general, but which later has been replaced by others. 

 It deserves to be mentioned in this connection that they appear together with 

 hyperstomial ooecia in Cribrilina punctata (PL IX). 



2) The hyperstomial ooecia (PL XXIV, figs. 12—18). These ooecia like the 

 endozocecial consist of an endoocecium and an ectoooecium, which join at the 

 free frontal edge of the ooecium and form together a fold, the ooecial fold: but 

 they are always situated outside the cavity of the zooecium, and the distal wall 

 does not take part in their formation, even though they most frequently arise 

 from or in the immediate neighbourhood of its frontal edge. The two layers 

 of the actual ooecium are formed by the frontal membrane of the distal zooecium, 

 but between these a cryptocyst layer may sometimes appear, and in many cases 

 the hyperstomial ooecia are provided with an ooecial cover. This type of ooecium, 

 which appears in the majority of the Cheilostomata, presents numerous modifica- 

 tions, of which we may mention here the most important, but for the rest refer- 

 ence may be made to the different families. 



We may begin with the ooecia in Scrupocellaria scabra, of which a series 

 of developmental stages have been figured on PL II, figs. 5 a — 5 f, as they 

 appear when the colony is viewed from the surface and after treatment with 

 boiling alkali or cold eau de Javelle. At the time when the frontal wall of the 

 distal zooecium is still quite membranous, the first trace of the ooecium appears as 

 two small dislal rounded calcareous plates, which arise from the frontal edge of 



