210 ISAO IIJIMA, 



its way toward the surface, the rays gradually diminish in 

 length. At the same time the curvature of the rays become 

 less and less conspicuous, until they are almost straight. 

 Fig. 18 is a stage in which the curvature of the rays is yet 

 retained to a slight extent. In fig. 19, which is a fresh 

 specimen, the rays can almost be said to be straight. In 

 this figure it is to be noted that the yolk-granules are 

 present even in the spindle, whereas in Clepsine (No. 7, 

 p. 14) the spindle is free entirely from the yolk-spheres. 

 From this fact I am rather inclined to think that the 

 spindle in the case of Nephelis is in a medium in no way 

 difierent from that in which the rays of the stars are situated* 

 Biitschli (No. 19) and some others seem to lay much stress 

 on the spindle. That it consists of the united rays of the 

 two stars accords with my observations, as well as with 

 those of Fol (Nos. 18 and 21), Bobretzky (No. 22), Whitman 

 (No. 7), and Mark (No. 2S) ._ 



Notwithstanding my special endeavours I have not been 

 able to get transitional stages between the germinal vesicle 

 and the archiamphiaster. But I was slightly successful 

 with later amphiasters directly concerned in the cleavage. 

 In fio". 20 is represented a divided egg, in which the 

 shrunken nucleus of each cleavage sphere is giving rise to 

 two stars. These stars belong to that amphiasler which 

 divides the egg into four. The left-hand sphere is less ad- 

 vanced than the other. On opposite sides of its nucleus 

 will be seen clear spaces, which are the polar areas. In the 

 rio-ht-hand sphere these areas are already surrounded by 

 radial rays. Here the upper star will be noticed as being 

 a little apart from the nucleus. 



What represents the nucleus of each cleavage sphere in 

 this fi"-ure is probably composed of a number of vesicles col- 

 lected in a group, as others of my preparations of the same 

 stage clearly show. The amphiaster which leads to the first 

 cleavage always gives rise to a group of nuclei in each 

 cleavage sphere, but I believe they do not necessarily 

 coalesce into a single body before they again dissolve 

 away. 



Such stages were also observed in the first cleavage 

 amphiaster. Here the male and the female pronucleus 

 ("Eikern") were placed close to each other in the centre of 

 an egg, and the stars were in process of formation on their 

 opposite sides. 



These stages of the amphiaster are probably to be 

 regarded as preceding the stage represented by Hertwig's 

 fig. 5 (Hsemopis, PI. I, No. 18). 



