36S THE GERM-PLASM 



to say, when they exactly correspond with regard to the time 

 and place of their ontogenetic origin and the number of their 

 determinants : but if this is not the case, such a ' reversion ' to 

 the characters of the other sex can hardly be possible, because 

 the foundation is wanting from which the reverted organ could 

 arise. Let us suppose that the same conditions as apply to 

 fowls hold good in the case of butterflies : — that is to say, that the 

 secondary sexual characters are present in a latent condition in 

 the soma of the other sex, and undergo development on removal 

 of the sexual glands. The male of LyccEua alexis, for example, 

 which has blue wings, would then develop brown ones on 

 being castrated. This w'ould take place by the shedding of old 

 scales and the growth of new ones ; or if castration had been 

 effected in the caterpillar stage, the scales in the growing wing 

 would be brown from the first. The scales are homologous 

 structures in the male and female, and each of them is controlled 

 by a single determinant. If, therefore, a cell containing the 

 determinant for a brown scale of the female is situated at the 

 base of the already developed scale of the male, a reversion 

 to the colour of the scales in the female might occur under such 

 circumstances, which are of course purely imaginary. 



The matter would, however, be entirely different if the female 

 LyccE)ia had no wings at all, as is the case in females of some 

 Bombycidce. The character of the blue scales in the male 

 would then have no homologue in the female, and an inactive 

 cell, with the determinant of a brown scale, could not possibly 

 be situated at the base of the blue scales in the male. This 

 may be expressed in general terms as follows : — doiible-detcr- 

 7nina)its, possessing a defi)iite ;nale and female character, can 

 only be present up to the phase and point in ontogeny in which 

 the development of the two sexes is exactly homologous. We can 

 therefore only expect a reversion to the secondary characters of 

 the other sex to occur when this point remains permanent. In 

 Lyccena the divergence would occur at the formation of the wing- 

 scales ; in Psyche (the female of which is wingless), in a certain 

 group of cells in the hypodermis of the thorax ; in Bonellia, in 

 all the cells of the larva ; and in the Rotifera, in the egg itself. 

 If our view is a correct one. a female Bonellia would conse- 

 quently be incapable of developing male characters in conse- 

 quence of castration, because it has long since passed that stage 

 of ontogeny in which the divergence into a male or female 



