STUDY OF CELL MECHANICS 469 



On the other hand, three independent workers (Wilson/01 a, 

 Ziegler '98 a and Mrs. Boveri) have reported that in enucleated 

 blastomeres in which asters were present, the latter have the 

 power of surrounding themselves with a certain amount of 

 protoplasm, and in one case (reported by Ziegler) of actually 

 dividing. While no mention is made here of the swelling of 

 the ectoplasmic layer or of cytoplasmic movement, it seemed 

 possible that both were present. In which case the chromo- 

 somes could not be regarded as causing the movement. 



The cytoplasm. A consideration of the above facts lead me 

 to take up the cytoplasm alone, as causing the movement. 

 The difficulty here was that supposing the swelling of the mem- 

 brane and the surface tension changes following were the result 

 of certain products produced by the oxidation of the cytoplasm, 

 then we should expect to find that the movement occurred in 

 all the eggs at the same time. This is far from being the case; 

 the egg protoplasm remains unchanged until certain processes 

 are completed in the chromosomes and aster, and this may 

 take place anywhere between the 2- and 8-cell stage of the 

 control. 



From the analysis of monaster eggs, it was clear that one 

 could not determine which, of the three possible factors, was 

 responsible for the protoplasmic movement, or whether per- 

 haps all three were involved. Further progress could only be 

 made when one or more of these factors could be eliminated. 



An attempt to eliminate the aster from the problem was 

 made by the use of the narcotic, phenyl ure thane. The re- 

 sults of the experiments are given below. 



EXPERIMENTS WITH NARCOTICS 



During the course of an experimental study in which the 

 eggs of Strongylocentrotus were treated with dilute solutions 

 of the narcotic phenyl urethane, T noticed that eggs left a long 

 time in this solution would finally undergo an irregular sort 

 of cleavage (figs. Hi to H 4 ). Furrows would appear in the 

 egg's surface preceded by a swelling of the ectoplasmic layer, 

 and two or more blastomeres would be cut off. Such divi- 



