300 



C. ISHIKAWA. 



dark granular mas.ses close to the nuclei. The protoplasmic connec- 

 tion (/>. c) is reduced to a narrow bridge. 



The changes which take place in the nucleus as well as details 

 ot the nuclear division will be spoken of in connection wi(h the pro- 

 cess of spore-fonnation. 



/). Spore-forniatiun. 



S[)ore-formation is always preceded by tlie concentration of the 

 central plasm into a rather small area, and liy the disappetu-ance of 

 all other structures, such as the tentacle, flagellum, teeth, etc. The 

 individual ap]'e:u's, therefore, as about to divide, except in not possess- 

 inf^' mouth and StahorijaH. Its central plasm is also raised a little 

 above the general surface of the body, and forms a low knob-like ele- 

 vation, as has been observed both by Cienhjirskii ( 89, p. 54) and, 

 by Hohin (6, p. 10()9). Just as in division, we find here a spherical 

 concentration of the granular cytoplasm about the nucleus, which is also 

 quite transparent in living specimens. Thus, Fig. 1 o, which is drawn 

 from an individual in this stage, shows the nucleus (/<) as a spherical 

 vesicle, while the archoplasm («) appears as a granular mass. The 

 division of the nucleus is also preceded here by that of the archo- 

 plasm, and we thus obtain a stage, represented in Tig. 14, which 

 exactly corresponds to the stage of di\'ision represented by Fig. 4. 

 In what direction the spindle lies in this case, it is not, however, pos- 

 sible to tell, as the external signs of the bilateral nature of the animal 

 can not all be recognised. The division proceeds still further, till 

 the stage is reached represented in Fig. 15 or 1(), the latter of which 

 is drawn from a living specimen. We sometimes meet with a sort of 

 partial segmentation of the entire body at this stage, the plane of 

 division cutting the connecting axis of the two nuclei, as has been 

 observed by Gienkowshj (7, p. 134). Fig. 17 represents a stage with 

 four nuclei, on the side of each of which is seen a. large archoplasmic 



