366 THE GERM-PLASM 



sation, while the female continues to develop, and reaches a 

 much higher stage of organisation, at any rate as regards many 

 organs, such as the nervous and vascular systems, which are 

 altogether wanting in the male. But neither is this the full 

 extent of the difference between them, for the testes, as well as 

 the skin and certain hooked organs of attachment are only 

 developed in the male at a later stage in a peculiar manner. 

 A certain correspondence still remains in the most essential 

 points of structure of the body, in spite of the great differ- 

 ence between the adult sexual animals ; so that, as Sprengel 

 says, the male is also ' a Gephyrean possessing all the known 

 structural characteristics of the group.' 



In terms of the idioplasm, this course of development may be 

 described somewhat as follows : the determinants which direct 

 the development of the larvae are single, and consequently 

 monomorphic larvae are produced. The idioplasm of all or most 

 of the cells, however, which constitute the organs of these larvae, 

 contain double determinants or double groups of determinants, 

 of which those for the female are, in most cases, far the larger : 

 in fact, the group for the female will usually not be opposed 

 by any for the male at all, — in the case, that is, of such organs 

 as the long proboscis, of which there is no homologue in the 

 male. It is certainly very remarkable that these groups of 

 determinants, although present in the male and unopposed by 

 others, do not become active ; but, even although we do not in 

 the least understand how it comes about that this inactivity is 

 enforced, the case is not more surprising than that of the deter- 

 mination of sex as a whole, and the inactivity of existing indi- 

 vidual primary constituents. Why do the wings first appear at 

 the pupal stage of the caterpillar, and not long previously, since 

 they must be present all along in rudiment — i.e.^ in the form of a 

 group of determinants in certain cells of the hypodermis? Or 

 why does a boy not grow a beard, seeing that the necessary 

 determinants must be contained in certain cells of the skin? 

 We can no more account for all these cases than for the in- 

 activity of sexually differentiated determinants. All that can be 

 "said is, that these determinants have the peculiarity of only 

 becoming active at a certain ontogenetic stage ; but this scarcely 

 gives any further insight into the matter than does the statement 

 that sexually differentiated determinants become active or remain 

 inactive, according to the sex of the organism in question. 



