62 



XVIII, figs. 13 a, PI. XXIV, fig. 15), besides in all members of the family Oncho- 

 poridae (Pt. XIII, figs. 6—9, PI. XXIV, fig. 12), and in both cases the whole 

 frontal wall of the ooecium is provided with such a layer, which is placed be- 

 tween the ecto- and endoooecium. There is however this difi'erence that while 

 this layer in Emballotheca arises high up from the cryptocyst of the distal zocecium, 

 in the family Onchoporidae it arises from the distal wall between the two zooecia. 



We very often in species of the genus just mentioned meet with the very 

 peculiar case, that the ooecium is formed by three to five adjoining zooecia and 

 consequently consists of the same number of segments meeting in sutures, of 

 which each single one includes a calcified endoooecial layer, a cryptocystic layer 

 and a membranous ectoooecial layer. 



We have seen that the basal wall of the ooecium in Scrupocellaria scabra 

 arises by calcification of a part of the original frontal membrane of the zocecium, 

 and nearly one half of the hyperstomial ocecia might be in a similar relation 

 to the zocecium, even though the size of this common wall for the zocEcium and 

 ooecium may be very variable in the different forms and sometimes present 

 considerable differences in species of the same genus. It seems as a rule to be 

 large in the families Membraniporidae, Scrupocellariidae and Petraliidae, as also in 

 the genera Escharella, Escharoides, Schizoporella, Escharina and Microporella, while 

 it is for example very small in Dendrobeania Murrayana (PI. IV, figs. 2 a — 2 e), 

 Porella compressa and Smittina trispinosa. In the genus Smittina especially the 

 relation between the zocecium and the ooecium seems to be subject to great 

 variations, and while the common wall in some species is large or of fairly con- 

 siderable size, e. g. in S. borealis, S. Smitti (PI. XIX, fig. 4 a), S. palmata (PI. 



XIX, fig. 5 a), it is as mentioned very small in S. trispinosa, and may again be 

 quite lacking in other species (S. reticulata, S. Lansborovi, S. linearis). In the 

 last case these ooecia, which we maj' call independent, consist of two layers in 

 their whole extent, and are formed by the ocecial fold alone, while this fold in 

 the previously mentioned cases arises in the circumference of a semi-circular area, 

 namely, the partition-wall between the zocecium and the ooecium. Such inde- 

 pendent ooecia seem to appear as a rule in the families Bicellariidae, Reteporidae, 

 Celleporidae, Mijriozoidae and Discoporidae, and they may also occur in the genera 

 Smittina and Porella (e. g. in P saccata); but as already mentioned there is 

 no sharp distinction between independent and dependent ooecia, because the 

 partition-wall may vary considerably in size. While the independent ooecia in the 

 above-mentioned Smittina species attach themselves so closely to the frontal wall 

 of the distal zocecium, that it is not possible to isolate them as a whole, the 

 hyperstomial ooecia in the family Bicellariidae on the other hand are freely pro- 



