COURTSHIP AND SEX 217 



functional modifications can be hereditarily entailed in some 

 representative degree. 



Surplusage Theory. — Hesse and Doflein have made the 

 interesting suggestion that as reproduction is very much less 

 expensive in the males, they have surplus material at their 

 disposal which may account for their frequently greater 

 variabiUty, for certain characteristics of habit and tempera- 

 ment, and for their exuberant growths of various sorts. 



Thus it is said of some humming-birds that the males 

 spend much of their time at the breeding season in fighting 

 and dancing, that they do not share in nest-building, brood- 

 ing, or feeding the young, that they play while the females 

 work. But it is easy to cite other cases where the male birds 

 do play a large part in the discharge of parental duties. 



To the objection that the male is often much smaller 

 than the female, and that his nutritive income will be pro- 

 portionally less, the answer is given that the decisive fact is 

 one of ratio, e.g. between the amount of material expended 

 in reproduction and the weight of the body in the two sexes, 

 or between the size of the reproductive organs and the size 

 of the body in the two sexes. 



In cases where the sexes expend approximately equal 

 amounts of material in reproduction, almost no sex-difi^er- 

 ences occur. Thus in many fishes, such as the herring, 

 the ovaries and testes are about the same size and enormous 

 quantities of milt are shed by the males in the water. In the 

 viviparous Cyprinodonts, on the other hand, where there is 

 internal fertilisation and economy of sperm-material, the 

 males show both permanent and periodic distinguishing 

 features. 



In his critique of the surplusage theory, Kammerer 

 indicates some serious, and indeed fatal, objections, {a) It 

 may explain how the male has a good deal to spend on 

 decoration, but it sheds no light on the specific line that his 

 expenditure takes — a mane for the lion and antlers for the 

 stag, {b) It is easy to pick out cases that suit the theory, but 

 what of the broad fact that in hundreds of cases among birds 

 and mammals, reptiles and insects, the two sexes are equal 



