304 JSfaohide Tatsu. 



II. Five enucleated fragments were cut from the egg imme- 

 diately after they were released and kept for an hour in the ster- 

 ilized water; first, in order to give the enucleated fragments 

 more time to ripen, so to speak, and second, for the sake of uni- 

 formity with the following experiment. Then the fragments 

 were transferred into the CaCK solution. After an hour they 

 were put back into the sterilized sea-water. In none of the 

 fragments did cytasters appear. 



III. (Control) Eggs were kept for an hour in the sterilized 

 sea-water. Meanwhile the germinal vesicle faded and the first 

 maturation mitosis reached the metaphase. Five enucleated 

 fragments were cut and treated in the same way as Experiment 

 A, a. In all the fragments cytasters were found. 



The above three experiments^ show clearly that the cytasters 

 do not appear in the enucleated fragments from the egg immedi- 

 ately after release. 



V. REVIEW OF LITERATURE. 



An experimental study of the cytasters was tor the first time 

 made by Morgan. In 1893 he saw refractile drops in the egg 

 of Arbacia treated with the sea-water to which a little NaCl 

 (2 per cent) had been added. In the winter of 1894-95 he extended 

 his experiments on the egg of Sphaerechinus to see if the refrac- 

 tile drops, which he later found to be the cytasters, cause the 

 division of cytoplasm. Although his expectation failed, yet, 

 from the studies along this line, he reached important results 

 which may be summarized as follows: 



^The following objection might be raised. The enucleated fragments for Experiments I and II were 

 smaller than those for Experiment III, and cytasters might not have been able to develop for this reason. 

 In fact, however, the former were only a little smaller than the latter; /. e., about the size of a fragment 

 represented in Fig. 12a. The minimal size of the cytoplasm which can produce cytasters is, I think, by 

 far smaller than any piece I used for the above experiments. In this connection I might cite a case in 

 which an egg was cut into three pieces, one nucleated and the other two enucleated. In one of the 

 enucleated fragments the aster was found. 



Another point: the eggs for experiment I and II were cut* as I stated expressly, immediately after 

 release. Sections of the normal eggs clearly show that a few asters do rarely appear after from twelve 

 to fifteen minutes' stay in sea-water, in spite of the fact that the nuclear membrane remains apparently 

 intact. The asters thus developed prior to the dissolution of the germinal vesicle, lie usually on or close 

 to the nucleus and very rarely far away from it. 



