THE ORIGIN OF GYNANDROMORPHS. 15 



if such an egg is fertilized by a male-producing Y-bearing sperm, it 

 produces a female XXY, that is like a normal female in its somatic 

 characters; but such a female, owing to the presence of three sex 

 chromosomes (XXY), gives rise to the phenomenon of secondary 

 non-disjunction to be described presently. 



Similarly in the male, primary non-disjunction may take place in 

 the formation of the spermatozoon. If at the reduction division the 

 X and Y chromosomes, that normally pass to opposite poles, should 

 pass to one pole, a spermatozoon would result from one of the daughter 

 cells that contains both an X and a Y, and such a sperm fertilizing 

 an X-bearing egg would give rise to an XXY female that would 

 exhibit secondary non-disjunction. The other daughter cell without 

 X or Y also produces a functional sperm. In these cases of primary 

 non-disjunction an irregular distribution of the sex chromosomes leads 

 to unusual types of sex-linked inheritance, but not to gynandro- 

 morphism or to mosaics. 



In secondary non-disjunction, owing to the presence of three sex 

 chromosomes, any two of which may form a pair, there is left one 

 chromosome without a mate. Genetic analysis shows that the un- 

 paired chromosomes, in some cases one of the X's, in others the Y, 

 may either pass out of the egg at maturation or remain in the egg. 

 Aside from this irregularity there is not much in the process that is 

 akin to the kind of chromosomal elimination postulated for gynandro- 

 morphs, since the processes underlying the two phenomena are prob- 

 ably quite different. These cases furnish exceptions in regard to 

 genetic behavior and furnish important evidence bearing on the deter- 

 mination of sex, but do not lead to the kinds of effects seen in the pro- 

 duction of gynandromorphs, except when the non-disjunction occurs 

 at a cleavage stage, as already explained. 



As stated, Boveri based his hypothesis of gynandromorph produc- 

 tion on an earlier observation that he had made with the sea-urchin 

 eggs. He found that occasionally the egg-nucleus began to divide 

 before the sperm-nucleus had fused with it. In consequence, the 

 sperm-nucleus fertilized, as it were, only one-half of the egg; i. e., 

 it approached one of the two daughter nuclei, and later became 

 incorporated with that one. In consequence, all the nuclei descending 

 from this fusion had the diploid number of chromosomes, while the 

 nuclei descending from the single daughter egg-nucleus had only the 

 haploid number. In the sea-urchin it has not been found possible to 

 raise plutei to maturity; hence the effect of this partial fertilization on 

 sex could not be determined. Boveri's application of this evidence to 

 gynandromorphs of the bee was purely theoretical, since at that time 

 the genetic evidence, that has since become available, did not exist. 



At about the same time Herbst carried out some experiments with 

 sea-urchin eggs that enabled him to produce a large number of em- 



