212 COMPARATIVE PHYSIOLOGY 



aspect of individuation is presented by the appearance of 

 sexual differences. In some animals, e.g. mammals and birds, 

 there is a sex metamorphosis (puberty). The effect of 

 castration in the male of mammals is too well known to call 

 for elaborate comment, and the work of Steinach, Lipschiitz, 

 Sand, Moore, and others definitely establishes between sexual 

 metamorphosis and the glandular constituents (the " interstitial 

 cells ") of the gonads, a relation analogous to that seen in the 

 phenomena just described. But there is no complete proof 

 that the interstitial tissue exerts its influence on metabolism 

 by discharging a hormone into the blood. The same remark 

 applies to birds, where spaying of the female leads to assump- 

 tion of male characteristics of comb, plumage and spurs ; and to 

 Amphibia. All the established phenomena are equally well 

 explained by the hypothesis suggested by Geoffrey Smith : 

 that is, the gonads quantitatively affect the metabolism of 

 one or other blood constituents by their own activity in situ. 

 Some reference is due to a conception introduced by 

 Goldschmidt because of its suggestive bearing on the general 

 consideration of time relations in development, and because it 

 at once disposes of any difficulty we might find in harmonising 

 the established role of genetic factors in sex- determination 

 with the undoubted facts of sex-reversal in the animal kingdom. 

 The production of intersexes in the gypsy moth, Lymantria, 

 by crossing local races has already been mentioned (p. 191). 

 In moths the sexual and somatic metamorphoses are synchro- 

 nous. The sex differences are very marked in the copulatory 

 devices, colour, wing pattern, feathering of the antennae, shape 

 of abdomen, etc. And intersexuality in Lymantria is not 

 an intermediate condition of sex differentiation affecting all 

 parts alike. The intersexual individual is a sex mosaic. 

 Females with a low grade of intersexuality may display modifica- 

 tion in the antennae alone, these being of the feathered, i.e. 

 completely male type. A higher grade of intersexuality is 

 seen when the wing-colour as well as the antennae are character- 

 istically male, all other organs being of the female type. The 

 most advanced stage of recognisable intersexuality is that in 

 which the individual is externally a perfect male but internally 



