CHROMOSOME GROUP IN BRACHYSTOLA MAGNA. 3/ 



must show that this particular chromosome does possess a power 

 not inherent in any of the others the power of impressing on 

 the containing cell the stamp of maleness, in accordance with 

 McClung's hypothesis. 



The evidence advanced in the case of the ordinary chromo- 

 somes is obviously more in the nature of suggestion than of 

 proof, but it is offered in this connection as a morphological com- 

 plement to the beautiful experimental researches of Boveri l al- 

 ready referred to. In this paper Boveri shows how he has arti- 

 ficially accomplished for the various chromosomes of the sea- 

 urchin, the same result that nature is constantly giving us in the 

 case of the accessory chromosome of the Orthoptera. He has 

 been able to produce and to study the development of blasto- 

 meres lacking certain of the chromosomes of the normal series. 2 



In larvae resulting from double-fertilized eggs which have 

 divided into three cells at the first cleavage, he recognizes an or- 

 ganism made up of definite thirds, each traceable to one of the 

 original blastomeres and each characterized, as a result of the 

 primary hap-hazard tripolar division, by a different combination 

 and generally by a different number of chromosomes from that of 

 its fellows. In rare instances such an embryo may be normal, of 

 which fact the possibility that each pole of the triaster may re- 

 ceive a complete normal series of chromosomes is explanation 

 enough. In other cases, the embryo may be completely normal 

 (for instance in respect to skeleton or pigmentation) in one or two 

 thirds, while in the remaining portion these structures may be 

 entirely lacking ; and it is a most significant fact that " in einzel- 

 nen dieser Falle konnte aus der Kerngrosse nachgewiesen werden, 

 dass die Grenze wo der Defekt beginnt, mit der Grenze zweier 

 auf verschiedene Ausgangsblastomeren zuruckfuhrender Bereiche 

 zusammenfallt." In the "normal' embryos mentioned above, 

 every part was present, and as regards specific characters, normal ; 

 but in different thirds there could be seen individual variations 

 which normally should have appeared in different larvae. " In der 



1 Boveri, /. c. 



2 By the normal series is here meant such a one as occurs in the nucleus of either 

 of the mature germinal products, since it has been clearly shown by the well-known work 

 on the fertilization of enucleate egg-fragments and on chemically induced partheno- 

 genesis, that either of the ripe germ-products possesses all the chromatin necessary 

 for the production of a normal larva. 



