102 THE ORIGIN OF GYNANDROMORPHS. 



logical evidence that can be adduced in support of this view is not 

 definitely established. 



Guyer's account of the ripening of the sperm and eggs in the fowl 

 is as follows: In the male there are 18 chromosomes, including two 

 Z chromosomes. After sj^napsis there are 9 double chromosomes in 

 the first spermatocytes, all of which except the double Z di\dde (or 

 separate), 9 going to one pole, 8 to the other. Thus one daughter 

 cell gets both Z's. This cell divides again, the Z's presumably separat- 

 ing, so that two second spermatocytes are produced, each with 9 chro- 

 mosomes (including the Z). These become the functional sperm. The 

 other daughter cell (without the Z's) may divide again, but it, or its 

 products, degenerate. 



In the female there are 17 chromosomes, including one Z. Pre- 

 sumably after reduction half of the eggs contain a Z and half are 

 without it. The Z-bearing egg fertilized by any sperm (each carries 

 one Z) will make a male with 18 chromosomes, including two Z's; 

 the egg without Z fertilized by any sperm makes a female with 17 

 chromosomes, including one Z. The scheme will account for the sex- 

 linked inheritance shown by the fowl. All genes carried by the two 

 sex chromosomes of the father will be transmitted to, and shown by, 

 his daughters, because each daughter gets her single sex chromosome 

 from her father. If the male carries dominant genes in his sex chromo- 

 somes, both daughters and sons will show the corresponding dominant 

 characters, etc. 



It is important to observe here that while this mechanism gives the 

 same results as to sex and sex-linked inheritance as the mechanism 

 described by Seller for moths, the actual process by which the two 

 end-results are reached are quite different in the male, although 

 presumably the same in the female. In the moth the reduction has 

 been worked out both in the male and female, while in the bird only 

 in the male. 



Five cases of gynandromorph have been described in birds, four of 

 which were bilaterally halved.^ Poll described a bullfinch that had 

 a testis on the right side, and this side had the red color on the breast 

 characteristic of the normal male ; on the left side there was an ovary, 

 and the left side of the breast was gray like the normal female. (See 

 frontispiece in Doncaster's book on The Determination of Sex.) 



Weber gives a full account of a finch, Fringilla coelehs, that had 

 the adult male plumage on the right side and that of the female on 

 the left side. The left side contained an ovary, the right a testis. 

 Weber states that Cabanis (Journ. fiir Ornithologie, XXII, 1874) 

 describes a "Dompfaffen" {Pyrrhula vulgaris) that was a bilateral 

 gj^nandromorph — on the right side male, on the left female. The bird 



^ Several mixed cases in hybrid pheasants and in Tetrao lestrix have been omitted here, as 

 well as references to "hermaphroditic" fowls. 



