THEORY OF DETERMINANTS 433 



Yet there was no hint of these in the queen bee herself. They 

 must have lain as latent elements in her inheritance. In the 

 case of plant-lice (Aphides) and some water-fleas (Daphnids), 

 where there is a succession of parthenogenetic females, the 

 primary constituents of masculine characters must remain latent 

 for several generations. In some cases — e.g. sea-urchins — the 

 sexes are so closely alike, even as regards their reproductive 

 organs, that we may almost say that they differ only in ' physio- 

 logical gearing,' and that to postulate one army of determinants 

 is sufficient without complicating matters by postulating at 

 least two analogous armies. But in the great majority of 

 cases there is marked dimorphism between the sexes, and, even 

 in the cases above referred to, it has to be remembered that 

 the spermatozoon itself is a very complex structure, with 

 apical piece, head, middle piece, tail, and other minutias, 

 many of which have no analogue in the ova, and are, indeed, 

 specially adaptive peculiarities which aid the spermatozoon in 

 finding the ovum. Thus it is difficult to escape Weismann's 

 conclusion that both kinds of sexual characters must be 

 present, some active, some latent, in every germ-cell and in 

 every organism. 



Another good example may be found in wheel-animalcules or 

 Rotifers, where the primitive germ-cells divide into two kinds of 

 eggs, externally identical, and yet so different that from the 

 one kind only females develop, and from the other kind only 

 males. Neither kind is fertilised. The ova which develop into 

 females must carry with them determinants corresponding to 

 masculine characters, though these remain quite latent, for 

 these females give origin to males as well as females. It may 

 be that nutritive and other environmental influences deter- 

 mine whether the determinants corresponding to the female 

 sex or those corresponding to the male sex become active ; 

 but the point at present is, that it is difficult to think out 



what occurs except on the hypothesis that the germ-plasm 



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