30 THE PHYSIOLOGY OF REPRODUCTION 



The tail of the lyre-bird, which is shed at the end of the 

 breeding season, not to be renewed again in the same form 

 until the following summer, the brilliant plumage of the breeding 

 drake, the more intense colouring of the phalarope, and many 

 other birds during the season of courtship, are famihar instances 

 of the same kind of phenomena.^ The remarkable plate of horn 

 which is developed in the upper mandible of the pelican in the 

 breeding season, and bodily shed at the end of it, and the " gular 

 pouch " in the throat of the breeding bustard, are examples of 

 a more special kind, the existence of which, however, must 

 be connected, either directly or indirectly, with the contem- 

 poraneous increase of sexual activity and the enhanced vitality 

 which accompanies it. 



In some animals certain glandular organs, apart from those 

 concerned in the reproductive processes, show a special activity at 

 the breeding season. For example, in the swiftlets (Collocalia) 

 the sahvary glands become peculiarly active, and secrete a sub- 

 stance which is aUied to mucin, and is employed in building 

 the edible birds'-nests of Chinese epicures.^ 



A somewhat similar pecuKarity exists in the male of the 

 sea-stickleback (Gusterosteus spinachia), which binds together the 

 weeds forming its nest by means of a whitish thread, secreted 

 by the kidneys, and produced only during the breeding season. 

 According to Mobius, as quoted by Geddes and Thomson,^ the 



g. of Nat. ffiat., vol. ix., 1902) draws attention to many such sexual 

 phenomena, and more especially to those occurring in the spawning season 

 in certain salmonoid fishes of the genus Onchorhynehus. The fish undergo 

 extraordinary changes in colour and shape, and, since they die when spawning 

 is accomplished, it is argued that the changes cannot have any sesthetic 

 significance but represent a pathological condition in which the fish become 

 continually more feeble and eventually succumb. 



• Beebe (" Preliminary Report on an Investigation of the Seasonal 

 Changes of Colour in Birds," Amer. Nat., vol. xlii., 1908) describes an experi- 

 ment in which certain tanagers and bobolinks, which had been prevented 

 from breeding, were kept throughout the winter In a darkened chamber 

 with a somewhat increased food-supply. As a consequence the nuptial 

 plumage was retained until the spriog, when the birds were returned to 

 normal conditions. They shortly afterwards moulted. The breeding plumage 

 was then renewed, so that in this case the dull winter plumage was never 

 acquired. 



2 Geddes and Thomson, Evolution of Sex, Revised Edition, London, 1901. 



^ Geddes and Thomson, loe. cit. 



