Some Experiments on Cell-division in the Egg of 

 Cerebratulus lacteus 



BY 



N. Yatsu. 



While making some experimental studies on the localization problem 

 in the egg of CerebrciUdus lad ens, in the summers of 1905 1 and 1907 I 

 observed certain facts which seem to thro.v some light on the mechanism 

 of cell-division. They will be described in the present paper under six 

 headings. 



1. Behavior of Enucleated Egg-fragments. 



a. with the aster. 



Case A. At an anaphase of the first division an egg was cut vertical- 

 ly parallel to the first cleavage plane. Soon after this operation the 

 egg divided to one blastomere of the normal size and smaller one (Fig. 1) 

 When kept in a compressorium the former became a morula, while the 

 latter did not divide at all (Fig. 2). The fragment cut from the egg also 

 remained undivided. In it no nucleus was visible, but two large asters 

 developed near the cut surface. From this it may be inferred that the 

 vertical cut separated the centrosomes from the chromosomes. In the 

 course of two hours a protuberance was formed on the enucleated fragment 

 on the opposite side to the asters (Fig. 2). The asters remained undivided 

 even as late as the 16-cell stage. It is interesting to note that the protube- 

 rance was formed at the farthest end from the asters as has been shown by 

 Boveri in the case of the monaster egg ('03). Furthermore the present 

 case seems to indicate that the above phenomenon takes place, (a) inde- 



i The work of the summer of 1905 was carried on under a gra-it from the Carnegie Institution 

 of Washington, to which I here express my great obligation. 



