Arti-ficial Parthenogenesis 172 Thalassema Mellita 143 



('02b, '05), on the other hand, has not only proved that Delage 

 erroneously determined the number of chromosomes in the fertil- 

 ized eggs of Strongylocentrotus to be 18, whereas it is 36, a blunder 

 which entirely vitiates his conclusion with respect to the chromatin 

 relations of his parthenogenetic sea-urchin larvae, but he has also 

 shown it to be highly probable that, in his experiments on merogony, 

 Delage was dealing with abnormal conditions which might easily 

 have led him into error regardingthe number of chromosomes present 

 in his embryos. Morgan ('95), moreover, several years before 

 Delage's work on merogony, had found the reduced number of 

 chromosomes persisting in early cleavage stages of fertilized enu- 

 cleated fragments of the sea-urchin's egg, an observation, how- 

 ever, to which Delage makes no reference. 



In a later paper on artificial parthenogenesis of Asterias glacialis, 

 Delage ('02c) states that a preliminary examination of his prepara- 

 tions has led him to believe that the number of chromosomes in the 

 morula and blastula is the same as in embryos arising from fertil- 

 ized eggs, that is, 18, but as he offers no evidence in support of the 

 statement, it cannot be accepted without further investigation. 



Although it is safe to conclude that the initial number of chromo- 

 somes persists, it must be borne in mind, as Boveri, Wilson, and 

 others have pointed out, that abnormal conditions may intervene 

 to disturb these relations and lead to a multiplication of chromo- 

 somes in a single cell, as may be seen, for example, in the case of 

 monasters and other pathological mitoses where longitudinal 

 splitting of the chromosomes may occur without accompanying 

 cleavage of the cytoplasm, as well as in eggs that have been entered 

 by supernumerary spermatozoa. 



The unusual conditions which I have described in the matura- 

 tion of the unfertilized eggs of Thalassema, whereby the cleavage 

 nucleus probably receives, not only the chromatin of the egg 

 nucleus, but that of one or both of the polar bodies as well, pre- 

 sumably lead to an increase in the number of chromosomes 

 throughout subsequent mitoses. This may be also true of Asterias 

 glacialis, since, according to Delage, the eggs of the starfish, like 

 those of Thalassema, may at times fail to extrude one or both 

 polar bodies. I have not been able thus far to prove that later 



