RELATIONS BETWEEN SEX AND INHERITANCE 473 



(b) The differences between man and woman, peacock and 

 peahen, ruff and reeve, stag and hind, lion and lioness, are so 

 conspicuous and manifold that we are apt to lose sight of the 

 primary distinction that the male is a sperm-producer and the 

 female an egg-producer. In the lower reaches of the animal 

 kingdom the two sexes are often superficially alike; it is as we 

 ascend the series that the primary differences have all manner 

 of secondary differences added to them. We hold to the central 

 thesis of The Evolution of Sex (1889) that there is a deep 

 constitutional difference between the male and the female 

 organism — a fundamental difference in metabolic gearing — the 

 female being relatively more constructive or anabolic, the male 

 relatively more disruptive or katabolic. This difference in the 

 organism is an expression of a similar deep initial difference in 

 the fertilised ova, which determines whether they get on to male 

 or female lines of development. The getting on to male or female 

 lines of development determines, late or early, whether the 

 detailed characters will find a masculine or a feminine expression. 



(c) In some cases, notably in insects, the differentiation of 

 the secondary sex-characters occurs at the same time as the 

 differentiation of the reproductive organs, and it cannot be said 

 at present that the latter influence the former. Both may be 

 simultaneous and independent expressions of the same initial 

 differences in the fertilised ova. 



In other cases, certainly, it is the saturating influence of the 

 early established maleness or femaleness that determines the 

 development of detailed parts, and of habits as well as structure. 

 A castrated pullet may acquire not only the outward structural 

 features of the opposite sex — cock's comb, wattles, long hackle 

 and tail feathers, rapidly developing spurs, carriage, etc. — but 

 the behaviour as well and the pugnacious character. There is 

 rapidly accumulating evidence of the importance of internal 

 secretions or hormones which pass from the reproductive organs 

 and exert a pervasive influence in development. One can argue 



