2i8 THE BIOLOGY OF BIRDS 



in size, equal in numbers, and uniform in appearance, 

 although the expenditure on the male's side is very much 

 less than the female's, (c) The female's reproduction is 

 more expensive, but yet it is the female that tends to fatten. 

 And why is it that when her reproductive expenditure is over, 

 her accessory sex-characters do not improve (except in rare 

 cases), but become less marked than ever ? (d) There are 

 many cases where the male has to fertilise the eggs of many 

 females, and where he has no masculine peculiarities, which 

 is what the theory would suggest. But there are also many 

 cases of a similar sort, where the polygamous male, like 

 peacock, pheasant, stag, bull, sea-lion, shows an exuberance 

 of masculine features. Indeed it has been suggested that 

 increased sexual function in the male tends to increase the 

 masculine features, and vice versa. 



D. Sex-Characters and Specific Characters, — Tandler and 

 Kammerer have done good service in showing that sex- 

 characters behave like ordinary specific characters, e.g. 

 in inheritance, in regeneration, and in their relation to 

 environmental influence. We think, however, that they 

 have exaggerated a useful idea, so that in its generalised 

 expression it becomes untenable. Tandler says : " All 

 secondary sex-characters were indeed at first specific cha- 

 racters . . . and not primarily associated with the genital 

 sphere." Thus the milk-gland has doubtless arisen from a 

 group of skin-glands, common to both sexes. Later on, 

 in the female, it came into the service of another function, 

 and under the influence of the reproductive organs. But 

 there is no enigma in its representation in the males. 



In Bovidae the possession of horns is a constant character 

 of a given species or variety. They are present in both 

 sexes. The shape- diflFerences between them form the sex- 

 character. When there is early castration, the two sexes 

 have the same kind of horn, which bears a marked re- 

 semblance to the ancestral type of Bos primigefiius . 



According to many authorities, antlers began as variations 

 on the part of the male Cervidae ; they necessarily became 



