142 George Lefevre 



linge des von Spermatozoon eingefiihrten Centriols sind. Die 

 von dieser Kegel statuierten Ausnahmen erweisen sich bei gen- 

 auerer Priifung als unhaltbar" (p. 429). In order to arrive at this 

 conclusion, he rejects all conflicting observations of others, in 

 many cases on entirely insufficient grounds. Griffin's account 

 for Thalassema is emphasized by Kostanecki as furnishing strong 

 support for his position, yet an examination of the same egg has 

 led me to seriously doubt the genetic continuity even in this case 

 between the sperm center and the centers of cleavage. 



In the light of my observations, therefore, it is difficult for me to 

 avoid the suspicion, at all events, that in the normally fertilized 

 eggs of Thalassema, as in those which develop parthenogenetically, 

 the cleavage centrosomes arise de novo and are caused to appear 

 in the egg cytoplasm upon renewal of those activities which lead 

 to the division of the cell. 



3 Numerical Relations of the Chromosomes 



It has been seen that the number of chromosomes (24) character- 

 istic of the fertilized egg of Thalassema is not restored during 

 parthenogenetic development, but that the reduced number is 

 retained throughout and has been repeatedly counted even in late 

 blastula and gastrula stages. This result is in accordance with 

 the observations of several others, who have determined the per- 

 sistence of the changed numerical relations of the chromosomes when 

 their number has been altered, as in the fertilization of enucleated 

 egg fragments and in artificial parthenogenesis, or under other 

 experimental conditions. This fact has been shown to be true by 

 Morgan ('95), Boveri ('95, '05), Wilson ('01) and Stevens ('02). 

 The parthenogenetic eggs of Thalassema, therefore, bear out the 

 contention, so strongly made by Boveri, that a restitution of the 

 normal number of chromosomes does not take place when the 

 number has been either increased or diminished by unusual con- 

 ditions. The fact, however, is opposed to the results which Delage 

 ('99, '01) has drived from his experiments on merogony and arti- 

 ficial parthenogenesis in the sea-urchin and which have led him 

 to maintain that the normal number of chromosomes is a specific 

 character and is restored when it has been disturbed. Boveri 



