SEX-CHROMOSOMES AND INHERITANCE 191 



character. It, or its normal allelomorph, should therefore 

 be present in both nuclei if all the chromosomes of the 

 fertilized egg have divided normally except the Z-chromo- 

 somes. This, in fact, has been found to be the case (Mor- 

 gan, Bridges, Sturtevant). 



Nearly all of the many hybrid gynandromorphs of 

 Drosophila can be explained as above. In a few cases, 

 when the abdomen of the fly was sufficiently female to 

 make mating possible, it has been found that the eggs give 

 the results expected for a female having the sex-linked 

 factors that entered the cross. 



FiQ. 88. — Diagram showing elimination of X' at an early cell-diviaion, so that the nucleus 

 to the right gets X and X' and that to the left only X. 



In a few cases in Drosophila the explanation of chro- 

 mosomal dislocation will not cover the results. Some of 

 these cases can, however, be accounted for by another 

 hypothesis. Should an egg arise with two nuclei (there 

 are several possible ways for this to occur), one nucleus 

 having one set of factors, the other the other set (the 

 parent being heterozygous), then if each nucleus is sepa- 

 rately fertilized a different combination of factors is pos- 

 sible from that possible on the elimination theory. A 

 gynandromorph, described by Toyama, appears to belong 

 to this category. Toyama found two gynandromorphs 

 of the silkworm (Fig. 89) whose mother belonged to a race 

 with banded caterpillars, and whose father belonged to a 



