No. 3.1 SEXUAL SELECTION IN SPIDERS. 137 



Accessory Plumes of Birds of Paradise Freqaentljj Arise from 

 Parts lohere Muscxdar Devebpvient is Inconsidcrahle. 



In view of the vital importance of this supposition to the 

 argument before us, the very life of tlie argument depending 

 upon its validity, let us examine carefully the evidence upon 

 which it is based. Do we find that all highly colored and 

 decorated birds agree in a proportion between the ornanienta- 

 tion and the nervous and muscular development of those parts 

 of the integument from which the ornaments arise? The 

 examples given by Mr. Wallace are not only few in number, 

 but seem to us to be misleading in character, since we find in 

 the very groups that he cites much more numerous instances 

 which go to prove the exact opposite. Look, for example, at the 

 birds of paradise. It is true, as he states, that in P. apoda and 

 P. minor the immense tuft of plumage springs from near the 

 great pectoral muscle, where muscular activity is at a maximum; 

 but to show that there is no causal relation between the mus- 

 cular activity and the plumes, we need only examine closely the 

 whole group of paradise birds, where we shall find that these 

 ornaments arise wherever they can be made useful for display, 

 and often from parts where there is no marked muscular 

 development. 



Thus the Great Bird of Paradise (P. apoda) lias two 

 elongated tail-feathers (34 inches long). 



The Red Bird of Paradise (P. rubra) has two elongated tail- 

 feathers (about 22 inches long), " which always attract attention 

 as the most conspicuous and extraordinary feature of the species" 

 (Malay Archipelago, p. 558). On the forehead, where the 

 muscular development is at its minimum, is a richly colored 

 double-crest. There are also tufts from the breast. 



The next species, the King Bird of Paradise (P. regia), be- 

 sides the breast-tufts, has " another ornament still more extra- 

 ordinary" (Malay Archipelago, p. 560); the two middle tail- 

 feathers are modified into very slender, wire-like shafts, which, 

 at their exti'emity, are enlarged and colored emerald green. 



We next come to the Magnificent Bird of Paradise (Diphyl- 



