11 



for, like the latter, they show large clear centers, their division was 

 actually observed in the living fragments, and more then one aster 

 "svas often observed in sections of single fragments. 



A possibility of error is undoubtedly introduced by the shaking 

 of the eggs to pieces; for it may well be that this somewhat heroic 

 treatment causes the escape of nuclear substance into the cytoplasm, 

 in the form either of minute portions of chromatin (which might 

 escape detection in the living eggs, or even in sections) or of achro- 

 matic constituents. The importance of avoiding this possibility by 

 cutting the eggs singly with the scalpel and treating the individual 

 fragments is obvious, and the experiment has in fact been performed by 

 Petrunkewitsch with results that appear to have been on the whole 

 negative. Against this negative result may, however, be placed the 

 positive ones (still unpublished) obtained by Mr. N. Yatsu, to which, 

 with his kind permission, I am able to refer. At my suggestion 

 Mr. Yatsu undertook the same experiment in the summer of 1903 on 

 the eggs of Cerehratulus (treated with CaCl2-solution) and on the very 

 transparent eggs oî EchinaracJmius (MgClo-treatment). In the first 

 named form, after individual section and isolation of the fragments, 

 six cases of aster-formation were obtained in the enucleated half upon 

 treatment with the solution; in the second, two such cases (out of 

 18 operated). In all these cases the asters were as conspicuous as in 

 entire eggs and developed large clear centers (characteristic of the 

 "true asters"); in three of them two asters were observed in each 

 fragment, though an actual division was not observed. It may be 

 added that in some of these cases the nucleated half divided, showing 

 that the egg-center had not been removed by the section; fixed and 

 stained preparations of the EchinaracJmius fragments (not however 

 sections) demonstrated the absence of a nucleus. These observations, 

 made with suitable sterilization precautions by a skilful experimenter, 

 are, I believe trustworthy and will be more fully reported hereafter, 

 Yatsu' s work being still unfinished. As yet these fragments have 

 not been sectioned to show the presence or absence of centrosomes; 

 but the character of the asters was that of »echte Strahlungen«, and 

 leaves no doubt that they were neither the 'primary radiation" nor 

 the small "artificial radiations" of the type described by myself and 

 Petrunkewitsch. 



It appears to me from the above that the work of Petrun- 

 kewitsch fails to overthrow or even to weaken the case for the in- 

 dependent new-formation of centrosomes in the entire eggs; and the 

 negative result attained in the case of enucleated fragments can not 

 be accepted as decisive against the positive ones of myself and Yatsu, 



