126 A. OKA. 



itself from the fiiniciilas and the other from the ectoderm. It is 

 needles,^ to say that in the aho\e light, a statoblast cannot he 

 a?)y thing else than a specially modified form of hud, in other words, 

 a t)ortion of both layers of the endocyst protected against severe 

 climate by special contrivances for the preservation of the species. 



But to return to the process of development, a certain nnmber 

 of cells, probably from tlie two sources referred above to, assemble in 

 the funicular lumen and arrange themselves into a group at first loose 

 and irregular. During this early stage, the funicular wall nowhere 

 shows thickening, contrary to Verworn's observations. Very soon 

 the group becomes compact and assumes a morula-like form. It can 

 now be safely asserted that new additions of cells no longer take 

 place, but that the morula henceforth increases in size l)y multjplic^a- 

 tion of its own cells. The mass bulges out the funicular wall as it 

 e id arges. 



Arrived at a stage when the morula measures about 0.05 mm. 

 in diameter, a certain nnml)er of cells (8-12 as seen in equatorial 

 sections) on one side of it form a special group (fig. 38, PI. XIX), 

 at first very indistinctlv distinguishable from the rest of the cells. 

 Graduallv, a small cavity appears in the rentre of that 8[)herica! 

 group of cells which are steadily increasing, changing it into a 

 hollow, rather flattened sphere with distinct epithelial wall. This 

 hollow sphere is the " cystogene Hälfte" of German authors, so called 

 on account of its giving rise to the chitinous covering of the stato- 

 blast, and the remaining mass of cells constitutes the " Bildungs- 

 masse." x\ccording to my observations, these two portions are not 

 morphologically distinguishable from each, other at a very early stage, 

 but become secondarily distinct. This is also the view held by Kitsche 

 and Yerworn, while Braem saw them originate sharply separated 

 from the outset in Cristatella. According to the last-mentioned 



