284 Mr Barrett-Hamilton, Secondary Sexual Characters 



such as that of Oncorhynchus the fatal result of the spawning 

 efforts is an acquired habit, the obvious use of which to the 

 species I have tried to show above. There seems to be no reason 

 why the plan adopted in the vegetable kingdom whereby we may 

 divide plants into annuals and those which live longer than one 

 year should not be equally successful amongst animals, so that 

 we may have in the same family examples of the annual in 

 Oncorhynchus, of the perennial in Salmo, with the additional 

 advantage that in the case of Oncorhynchus the death of the 

 parent supplies the offspring with food. 



But I conceive, that once the existence of such a primitive 

 state of things characterised by growth or discoloration of the 

 whole or of part of the body is admitted we have therein the 

 starting point whence Natural Selection by alteration, suppression 

 or accentuation of the details, might easily produce many or all 

 the nuptial changes of animals as we now see them, evolving in 

 each a structure suitable to its own particular need, whether in 

 eye as in the Eel, in snout as in the Salmon, or in hind-limb as 

 in Lepidosiren. 



The originally temporary assumption of colours or outgrowths 

 under the influence of the activity of the generative organs might 

 recur annually or be fixed as a permanent characteristic of one 

 or both sexes of a species according to the need of each particular 

 instance. Such colours or outgrowths need not, however, lose 

 their connection with the generative organs, and thus (as is 

 actually the case in many instances) would appear only when the 

 development of these organs reached a point such as to influence 

 the general metabolism of the body. They would therefore be 

 absent during immaturity. Thus in most birds the breeding 

 plumage differs from that of immaturity or of seasons when the 

 generative organs are quiescent, and is only assumed and worn 

 during the periods of activity of these organs. In many species 

 it is probable that the occurrence of such changes in the breeding- 

 season may have, under the constant action of Natural Selection, 

 been altered or suppressed to such an extent as to be now un- 

 recognisable, although such influence may possibly be traceable 

 in the moults which so usually precede or follow the breeding- 

 season, and which are not necessarily restricted to the casting off 

 of hair and feathers, but may include the shedding of the horns, 

 as in certain Ruminants, of the claws, as in some of the Tetra- 

 onidae, or of portions of the horny mandibles, as in the Alcidae 1 . 



It would seem to be a logical deduction from my theory, if 

 it be correct, that both sexes should normally be the same in 



1 The curious seasonal changes in the forefeet of Dicrostonyx (= Cuniculus) may 

 be analogous : see G. L. Miller, Junior. " Genera and Subgenera of Voles and 

 Lemmings " {North American Fauna, No. 12, July 23, 1896, p. 89). 



