RELATING TO SECONDARY SEXUAL CHARACTERS. 47 



above the point where the arteries and nerves for the supply of the 

 pectoral muscles, and neighboring regions, leave the interior of the 

 body. The area of attachment of the plume is, also, as you say in your 

 letter, just above the junction of the coracoid and sternum." "Orna- 

 mental plumes of considerable size rise from the same part in many 

 other species of paradise birds, sometimes extending laterally in front, 

 so as to form breast shields. They also occur in many hummingbirds, 

 and in some sun birds and honey-suckers; and in all these cases there 

 is a wonderful amount of activity and rapid movement, indicating 

 a surplus of vitality, which is able to manifest itself in the development 

 of these accessory plumes." 1 



There are two serious defects in such an attempt to explain the facts. 

 In the first place, it has been shown in several cases that have been 

 studied that it is not the lessened "vitality" of the female but the suppres- 

 sion caused by the ovary that keeps down the development of the full 

 plumage in that sex. In the second place, the anatomical influences 

 appealed to are imaginary rather than real, for it is by no means 

 apparent that the local exits of blood-vessels and nerves to muscles 

 are at all correlated with the location of the ornamental parts, in the 

 skin. Even when larger blood-vessels run to the region of excessive 

 development of feather ornaments it may well be that they go there 

 because the ornaments in question use them for their nourishment; in 

 other words, Wallace puts the cart before the horse. The top of the head, 

 where crests so often develop, the throat coloration and throat shields 

 of hummingbirds and birds of paradise, the two long tail feathers of 

 several species of hummingbirds, etc., do not arise, so far as known, 

 from regions which are conspicuous for a rich supply of blood and 

 nerves. Wallace's appeal to underlying organs such as muscles that 

 supposedly influence the special development of the feathers in the 

 skin above does not strike one as a fortunate appeal to physiological 

 principles. 



Hudson, in his interesting book, "The Naturalist in La Plata," has 

 also criticized Darwin's theory of sexual selection. He has brought 

 together a considerable number of interesting observations that go to 

 show that the displays dancing, singing, and combats of males and 

 females have no relation to mating. Many of them involve birds 

 already mated, sometimes several males participating, sometimes 

 males and females together. Some of the tourneys he describes are 

 more elaborate than the mating instincts themselves, yet are not con- 

 cerned with mating. He attempts to explain them as overflow phe- 

 nomena, i. e., as expressions of the high vitality of the males, especially 

 at this time. If he is right, then elaborate exhibitions of these kinds 

 have evolved that have no special connection with mating. Are we 



1 For activity and pugnacity in hummingbirds, see Tropical Nature, pp. 130, 213. 



