Centrosome m Enucleated Egs[-Fragiiunts. 307 



up into fragments, the membrane of the egg-nucleus may be torn 

 and consequently the cytasters are formed by the intermingling 

 of the nuclear fluid and cytoplasm. 



Meves ('02, <?, b^ and '03) thinks that the cytasters may arise 

 in the following way: Numerous centrioles may be handed 

 down to the egg from the last division of the multiplication period 

 somewhat as in the formation of the oligopyrenous spermatozoon 

 in Paludina. He, therefore, holds the view that cytasters may be 

 derived from preexisting centrioles which have acquired a new 

 ray system around them by the action of salt solution ('02, a, 

 p. 155). He criticises Wilson's experiment on enucleated frag- 

 ments on a ground slightly different from Wassilieff's objection, 

 assuming that, even if there be no preexisting centrioles in the 

 cytoplasm, the egg center may by shaking be thrown off in the 

 enucleated fragments ('02, a, p. 155). 



It was in order to test the above two possibilities that Professor 

 Wilson suggested to me two years ago to repeat his experiment on 

 enucleated fragments by cutting unfertilized eggs in two singly 

 and to treat the enucleated piece with some salt-solution. This 

 I tried both in the egg of Cerebratulus lacteus and of Echina- 

 rachnius parma^ in the summer of that year. 



In the meantime appeared Petrunkevitsch's paper on artificial 

 parthenogenesis ('04). He took up the same form as that studied 

 by Wassilieff, Strongylocentrotus lividus, in which I fully realize 

 how difficult the fixation of the centriole is. Surprisingly enough 

 Petrunkevitsch was led to the conclusion that in the egg of this 

 sea-urchin there is no centriole at all (p. 32).^ His whole argu- 

 ment, therefore, applies to the centrosome not to the centriole. 

 He denies the formation de novo of the centrosome and tries to 

 rescue Boveri's idea of continuity of the centrosome. He came 

 to this conclusion from the study of sections of the eggs, the 

 "stages" of which were selected arbitrarily. Despite this he 

 insists that his view regarding the origin of cytasters is thus con- 



^In the egg of this echinoid I used the following solution: 11.8 per cent of MgCl2 ( = -?" "^- MgClo), 

 I part; sea-water, i part. In two cases out of eighteen fragments the cytasters were formed. Total 

 preparations of these two pieces showed that they had no nucleus in them. In passing I should state 

 that the following solution is the best to induce parthenogenesis in the egg of Echinarachnius: 18.6 per 

 cent of KCl {=^i'- m. KCl), 15 parts; sea-water, 85 parts. 



^Noteworthy is the fact that, judging from his figures, he actually saw the centrioles, but mistook 

 them for reduced centrosomes (not in Boveri's sense), e. g., PI. 2, Fig. 24. 



