GrEOFFREY Smith and Mrs Haig Thomas 43 



between the seventeenth and nineteenth day of incubation. After 

 synapsis the chromosomes separate and the nuclei pass back into the 

 vegetative phase until polar-body formation. Now it is perfectly clear 

 from the foregoing facts that since in the normal female it is necessarj- 

 for the oocytes to undergo the synaptic phases before they can store 

 yolk and grow up into mature oocytes, we must conclude that in the 

 case of the sterile hybrids this early synapsis was initiated, but owing 

 to the incompatibility of the chromosomes it failed to take place 

 normally, with the result that the oocytes failed to grow. 



The fact, therefore, of this early synapsis in the female germ-cells, 

 gives us a complete explanation of why the germ-cells degenerate in 

 the female at an apparently earlier stage than the germ-cells in the 

 male. In reality the germ-cells begin to degenerate and become ab- 

 normal at exactly the same phase in both male and female hybrids, viz. 

 at the synaptic phase, so that the generalization that the sterility of 

 hybrids is due to the incapacity of the chromosomes derived from two species 

 to form the normal synaptic pairs applies to both sexes of hybrids, and is 

 probably of universal application. 



2. The assumption of male characters by sterile females. 



The sterile females examined under this head include four Common 

 Pheasants (A, G, B and E), which were probably all crosses between 

 P. torquatus and colchicus ; a sterile pure-bred Formosan variety of 

 P. torquatus (K) ; a female hybrid between Reeve's $ and versicolor 

 J" (M), and two hybrids between Reeve's $ and Formosan J' (B 

 and G). 



The Common Pheasants A, G, D and E will be dealt with first. 

 These were all young birds, shot probably in their first winter, and 

 dissection revealed an identical condition in all of them, viz. entire 

 absence of any visible ovary or gonad of any kind, and the presence of 

 a very small, narrow oviduct on the left side which had its opening into 

 the cloaca occluded, and the other end narrowing down to a fine fila- 

 ment. I was unable to detect any trace of germinal tissue in any of 

 these birds; otherwise they appeared healthy and normal. All four 

 birds showed male characters in the plumage to slightly varying 

 extents. In all of them the neck feathers, both dorsally and ventrally, 

 but especially the former, have a large part of their distal borders 

 metallic green, as in a cock bird. These neck feathers show distinct 

 traces of the white ring characteristic of P. torquatus ^. The feathers 

 of the back are of normal female appearance ; and so are the wing 



