58 



a strong flexion and alteration in shape. Thus, while the angle between the hori- 

 zontal and vertical portions of the distal wall in fig. 8 b is right, and in fig. 8 c 

 obtuse, it gradually becomes more and more acute on account of the endoooecium 

 bending backwards towards the basal wall of the zooecium, without doubt be- 

 cause of the counter pressure brought about by the growth-tension. While the 

 portion between the horizontal part of the distal wall and the point of the 

 indentation has nearly the same length in the examined longitudinal sections, 

 the indentation on the contrary increases in length, and lastly the ooecial fold 

 grows down over the ooecial membrane, which not long before occupied most of 

 the frontal wall of the developing ooecium. At the same time as the developing 

 ooecium is undergoing these alterations in shape, the whole zocecium increases 

 considerably in size, and the horizontal part of the distal wall in length. 



As already mentioned in the above reference to V i g e 1 i u s ' investigations, he 

 believes that the ooecial membrane dissolves later, so that the egg from the zoce- 

 cium can reach into the ooecium, but this view clearly proves to be wrong from 

 the fact, that I have found eggs lying in the ooecia in Fl. securifrons and Fl. 

 meinbranaceo-truncata (PI. I, fig. 2 a), the floor of which is formed by such an 

 ooecial membrane on which the egg rests. The egg must therefore have come 

 into the ooecium from outside through the ooecial aperture, and possibly the 

 altered position of the ooecial membrane is due to this transference. Figs. 8 g — 8 n 

 show a series of developmental stages of the ooecium mentioned, seen from the 

 surface of the colony. In the earliest of these (8 g) the ascending part of the 

 distal wall has not yet begun to calcify, and the deep sinus between the two 

 rounded projections comes from the not yet closed uniporous rosette-plate. The 

 other figures show the formation of the ooecial bladder, its partial closure and 

 the formation of the two calcareous ribs. 



While the rest of the ooecium-bearing members of the family have essentially 

 the same 'Structure of the ooecia as Fl. securifrons, we find a rather different 

 structure in Fl. foliacea (PI. I, figs. 8 a, 8b; PL XXIV, fig. 8), as the ooecia here 

 have an irregular egg-shape. Whilst, as already mentioned, a pair of cryptocyst- 

 ribs occur in Fl. securifrons proximally to the operculum of the zooecium, in a 

 number of species, e. g. in FL membranaceo-truncata (PI. I, figs. 2 a, 2 b, PI. XXIV, 

 fig. 6), Fl. Barleei (PI. I, fig. 3 a), Fl. Schonaui (PI. I, fig. 7 c) etc., a more or 

 less developed cryptocyst-belt occurs just distally to the free edge of the ooecium, 

 between this and the covering membrane; the originally separated lateral halves 

 of this belt later fuse together. This belt reaches its highest development in Fl. 

 flastroides (PI. I, fig. 4 a; PI. XXIV, fig. 7) and it may in time quite cover the 

 ooecia, which in this species exceptionally project distinctly on the surface 



