426 Hawkins, Sexual Selection and Bird Song. [ " t 



of body (or to use the medical terra, diathesis), as that which results 

 in the production of male elements in the one case, or female ele- 

 ments in the other." 



This essential difference between the two sexes which expresses 

 itself in differences of plumage and song is further emphasized by 

 the facts, first, that many of the secondary sexual characters 

 appear only at sexual maturity. Thus some of the male birds are 

 dull colored when young like the female and acquire the brighter 

 colors only on full development. Again when the sex organs are 

 removed by castration the male ornaments or weapons of battle 

 disappear. In cattle castration reduces the size of the horns and 

 after castration of the stag he never renews his antlers. 



In the case of young cocks the effects of castration are very 

 variable, sometimes increasing, sometimes decreasing the secondary 

 sex characters. One result is clear, however, that the whole body 

 is affected; the larynx is intermediate in size between that of cock 

 and hen, the syrinx is weakly developed and the capons seldom 

 crow or do so abnormally, the brain and heart are lighter in weight, 

 fat accumulates in the subcutaneous and subserous connective 

 tissues, and the skeleton shows many abnormalities. 



The conclusion seems inevitable that neither Darwin nor Wallace 

 reached the root of this matter. "The males are stronger, hand- 

 somer, or more emotional, simply because they are males, i. e. of 

 more active physiological habit than their mates." This view 

 does not wholly eliminate either natural or sexual selection. These 

 may be limiting, and, in a sense, directive factors, but it is funda- 

 mentally the nature of sex which determines the gay color or the 

 vigorous song. 



To complete our review of this controversy which has been 

 waged between ornithologists, we must record some of the more 

 recent discussions of the Darwinian theory of sexual selection. 

 Hudson says; "The result of such independent investigation will 

 be a conviction that conscious sexual selection on the part of the 

 female is not the cause of music and dancing performances in birds, 

 nor of the brighter colors and ornaments that distinguish the male. 

 It is true that the females of some species, both in the vertebrate 

 and insect kingdoms, do exercise a preference; but in a vast 

 majority of species the male takes the female he finds, or that he is 



