63 



jectiiig, so that they can very easily be separated and the same is the case with the 

 ooecia in the genus Thalamoporella and in most species of the genus Discopora, 

 although to a less extent. In the family Reteporitlae also the oa^cia seem origi- 

 nally always to be free and able to be isolated, even though they later get tirmly 

 imbedded in the colony by covering layers, and they seem here, as in the family 

 BicelUiriitldc, always to be provided with a narrow, almost stalked basal part, as 

 is also the case with the Od'cia in Porclhi sdccota. 



While the frequently mentioned wall between the zooecium and the ou'ciuni 

 in Malacoslegous forms only consists of a gymnocystic layer, it is on the other 

 hand as a rule wholly or partly two-layered in the Ascophore forms which have 

 a cryptocyst, as within the gymnocyst there is a cryptocystic layer, which some- 

 times covers its whole surface, sometimes only a larger or smaller part of it. 

 This difference seems to depend on how far the ocecium appears at an earlier 

 or later stage of development of the zoa'cium. In species of the genera Schizoporella, 

 Escliarina, MicroporelUi, Petralia and Emlxillotlieca, besides in certain species of 

 the genus Sinittina (5. Lansborouii, S. reticiilala and .S. linertris) the ooecia first 

 appear after the frontal wall of the zooecium is comjjletely formed, so that the 

 basal wall of the oa'cium, which arises by calcification of a portion of the frontal 

 membrane, comes in its whole extent to lie up against the cryptocyst of the 

 frontal wall, from which, however, as a rule, it seems fairly easily detachable. In 

 Emballotheca furcala at the place where an otrcium is going to be formed, we 

 find a deepened, semicircular area, surrounded by a low marginal ridge, and a 

 similar deepened area might also be found in species of the genus Petralia (PI. Will, 

 fig. 5 a), as the ooecia here are in their basal half sunk into niche-like recesses. 



On the other hand, in the genera Escharella (PI. XVII), Escharoides (PI. XVII), 

 as also in certain species of the genera Porella (e. g. in P. slriima Norman and 

 P. glaciata Waters) and Sinittina (S. Sinitti, S. Iwrealis, S. palmata etc.) the rudi- 

 ment of the oa^cium, as in Scriipocellaria scalna, is seen at a very early stage in 

 the development of the zocecium, and the cryptocyst, which from the beginning 

 only appears outside or in the marginal region of the basal wall of the ooecium, 

 as a rule gradually grows more or less far in over the basal surface, which as 

 a rule however has a larger or smaller triangular, semicircular or semielliptical, 

 proximal area which is not covered by the cryptocyst. In contrast to what lakes 

 place in the genera Schizoporella, Escharina etc. this cryptocystic layer is here 

 firmly fused together with the gymnocyst wall of the oa-cium, and it is in rare 

 cases, as in Escharoides coccinea and E. Jacksoni, provided with wide pore-canals. 



While a calcified ectoooeciiim does not seem to increase in thickness, and this 

 is also the case with the endooa'cium when it is covered bv a calcified ectoori'cium, 



