Introduction: Variation. 
69 
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 Turnioo nigricolUs^ 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 Jerdon’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 Tiirnix^ by an excess of reproductive power. 
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 species 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 wUlch can distinguish one 
another (Theory 7). 
6. ^) Protective coloration for the sex which broods on the eggs (Theory 4). 
1) A rudimentary right ovary is usually present (Gradow, Yog. in Bronn’s Kl. u. Ord. 1891, p. 842). 
2) As to Darwin's theory of sexual selection authors are disagreed. 
