HEREDITY. 315 



distinctive of sex, such as the beard and the voice in man, 

 we have numerous cases in which, along with different sex- 

 organs there go general differences, sometimes immense and 

 often conspicuous. We have those in which (as in sundry 

 parasites) the male is extremely small compared with the 

 female; we have those in which the male is winged and the 

 female wingless; we have those, as among birds, in which 

 the plumage of males contrasts strongly with that of females ; 

 and among butterflies we have kindred instances in which the 

 wings of the two sexes are wholly unlike some, indeed, in 

 which there is not simply dimorphism but polymorphism: 

 two kinds of females both differing from the male. How 

 shall we range these facts with the ordinary facts of inheri- 

 tance? Without difficulty if heredity results from the pro- 

 clivity which the component units contained in a germ-cell or 

 a sperm-cell have to arrange themselves into a structure like 

 that of the structure from which they were derived. For the 

 obvious corollary is that where there is gamogenesis there 

 will result partly concurring and partly conflicting proclivities. 

 In the fertilized germ we have two groups of physiological 

 units, slightly different in their structures. These slightly- 

 different units severally multiply at the expense of the nutri- 

 ment supplied to the unfolding germ each kind moulding 

 this nutriment into units of its own type. Throughout the 

 process of development the two kinds of units, mainly agree- 

 ing in their proclivities and in the form which they tend to 

 build themselves into, but having minor differences, work 

 in unison to produce an organism of the species from which 

 they were derived, but work in antagonism to produce copies 

 of their respective parent-organisms. And hence ultimately 

 results an organism in which traits of the one are mixed 

 with traits of the other; and in which, according to the pre- 

 dominance of one or other group of units, one or other sex 

 with all its concomitants is produced. 



If so, it becomes comprehensible that with the predomi- 

 nance of either group, and the production of the same sex as 



