Introduction: Variation. ^Q 



with Beddard's theory, the reduction in size and the quiet disposition of the 

 male bird should be due to the partial atrophy of the male organs. Beddard's 

 theory here seems to contain the most probable explanation, and it would be 

 well to make observations on other Centropodinae. It still remains to be demon- 

 strated how such an aberration has arisen, which is perhaps comparable to the 

 development of only the left ovary' in the female of all birds. 



In the case of Turnix nigricollis, in which the male does most of the work of 

 incubating the eggs, the large and strikingly coloured female is supposed from 

 observations by Mr. Krohn (Getied. Welt, 1894, 190) to be given to polyandry. 

 Darwin cites Jer don's remark that the females are "much more commonly 

 met with than the males". It is difficult to reconcile this statement with the 

 former supposition, but these cases are mentioned here as showing that the 

 contrast in size, habits, etc., may sometimes, as in Centrococcyx, be accompanied, 

 and perhaps determined, by a deficiency of reproductive energy or capacity, or 

 sometimes, as perhaps in Turnix, by an excess of reproductive pow-er. 



In addition to the 6 theories of the origin of secondary sexual characters 

 mentioned above at least two more can be indicated. 



7. Secondary sexual characters as "recognition markings". Mr.Wallace 

 (Darwinism, 1889, p. 217 et seq., and in other works) seems to have been the 

 first to define conspicuous markings and patches of colour as useful means by 

 which individuals of a species may at once recognise others of their own kind. 

 He applies his theory to sjjecies and further on (p. 284) to the sexes. 



8. Development of accessory sexual characters owing to external 

 violence or excessive physiological employment of the parts in question. 

 Use promotes the development of a part in the individual, disuse its atrophy. In 

 the next section of this chapter reason is also given for the opinion that mutilations 

 of feathers — and hence of other parts — if repeated for generations are inherited. 



In the present case out of 8 theories of the origin of secondary sexual 

 characters it may well be that 6 have been actually operative in Nature, work- 

 ing alone or more likely in different combinations and degrees. These 

 causes are: 



1. The differences of the reproductive organs (Theory 6). 



2. Higher development owing to a prepotency of growth-force (Theory 3). 



3. Survival of the fittest in combat (Theory 2). 



4. The stimulation of parts to a higher development by use and external 



violence or irritation (Theory 8). 



5. Development of recognition -characters by natural selection and pre- 



ferential mating of males and females which can distinguish one 

 another (Theory 7). 

 6.-) Protective coloration for the sex which broods on the eggs (Theory 4). 



>) A rudimentaiy riglit ovary is usually present (Gadow, Yog. in Bronn's Kl. u. Ord. 1&91. p. S42,. 

 2} As to Darwin's theory of sexual selection authors are disagi-eed. 



