OTHER THEORIES OF SEXUAL COLOURING 325 



The objection to Mr. "Wallace's explanation of the 

 immense tufts on Birds of Paradise 



Mr. Wallace, however, follows up this idea, and 

 argues that ' the immense tuft of golden plumage in 

 the best known birds of paradise * is related to the 

 proximity of the most powerful muscle in the body 

 (the pectoral), of certain large blood-vessels and 

 nerves, and of certain parts of the skeleton. The 

 contractions of the muscle mean of course a great 

 expenditure of energy, but the present state of phy- 

 siology lends no support to the opinion that such 

 expenditure could afford any explanation of the size and 

 special peculiarities of an appendage produced by an 

 adjacent surface. The nervous and arterial trunks 

 imply that nervous energy and food material are 

 being conveyed in large quantities to the localities 

 where the nerves and arteries are finally distributed ; 

 but their size and importance as they pass beneath 

 the base of the tuft can have no relation to the growth 

 and appearance of the latter. The travelling facilities 

 and means of communication in any village depend 

 upon the local arrangements of its railway station and 

 telegraph office ; not upon the number of express- 

 trains and telegrams which rush through it on their 

 way to a distant town. 



