C. J. Bond 211 



secondary sex characters in the body as a whole, and there can I think 

 be little doubt that this depends on some important law of ontological 

 development in birds. In the head and neck, trunk and limbs, the 

 development of the pigmentary pattern and feather structure seems to 

 be under the control of separate unilaterally acting factors, whereas 

 in the tail (at any rate in some birds) one single factor controls 

 the development of the tail as a whole, and this single factor may 

 differentiate later into secondary factors which control the development 

 of each half of each tail feather, as in this case. 



There are some interesting facts in neural physiology which bear on 

 this point. Langley and others have shown that unilateral stimu- 

 lation of the central nervous system produces unilateral action in the 

 sympathetic pilo-motor fibres which supply the trunk and limbs, whereas 

 in the tail the effect of the unilateral stimulation passes over the middle 

 line and affects the tail as a whole in the cat. 



Rorig of Frankfort has recorded cases in which unilateral castration 

 in the stag has been associated with abnormal growth of the antler on 

 the opposite side of the body, and other cases of injury to the fore leg 

 with arrested growth of the antler on the same side, and cases of injury 

 to the hind leg with arrested growth of the antler on the opposite side. 

 There is a specimen in the Royal College of Surgeons Museum which 

 shows the same thing. The question of the influence of unilateral 

 castration and unilateral injury on antler growth would well repay 

 further inquiry. It is possible that secondary sex characters in the 

 stag are peculiarly sensitive to nervous influences, and it would seem 

 at any rate that if Rorig's observations are confirmed they cannot be 

 entirely explained by any purely Hormonic theory. 



It is interesting to compare this hemilateral feather pattern in the 

 tail of this hermaphrodite bird with a case described by Shattock and 

 Seligman in the Transactions of the Path Soc. LVII, 1906, where they 

 figure the tail feather of a cock pheasant hatched in 1902 (cf. PI. XI, 

 fig. 14). At Christmas 1903, this bird, while showing the usual adult 

 male plumage, began to develop female markings at the proximal end of 

 the central tail feather. This localized assumption of a secondary female 

 sex character did not come about through the moulting of the male 

 feather and the growth of a female one, but by the appearance of the 

 female pattern at the base of the male feather. The portion of the 

 feather so marked was sharply divided transversely from the male portion 

 and included the whole width and both sides of the feather. During 

 subsequent moults in 1904-5 there was no reappearance of the female 



