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JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol. XVI. 



proclivities. They expressed the contrast in the sexes as an antithesis between 

 a relative anabolic and a relative katabolic preponderance in the protoplasmic 

 life of the creature. They directed attention to the large size and more 

 sluggish nature of the ovum and the smaller size and more active nature of 

 the sperm; these are essentially anabolic and katabolic features. For the 

 fertilisation of a single ovum a single sperm cell is only necessary ; but in the 

 process many sperm cells (often thousands ) are involved, all, save the single 

 necessary one, are dissipated, broken up, and lost. The katabolic tendency in 

 the male element is very marked in this inslance. Males essentially dissipate 

 energy, females conserve it. Now we all know how important a relation exists 

 between the generative or sexual and the vegetative cells. Stimulation of the 

 former reflects itself in the latter. It is undoubtedly this katabolic stimulation 

 of the veg3tative cells, communicated through the male generati\e cells during 

 the rutting season in certain animals, which makes the males so fierce, energetic, 

 and destructive. The katabolic stimulus communicated to the vegetative cells, 

 through the male generative cells may be dissipated in various forms of energy — 

 e. g., excessive growth, excessive bodily and nervous activity, and, as I hope to 

 show, excessive brilliancy of colour. 



This katabolic stimulus of the male generative cells on the vegetative cells is 

 the fundamental cause of sexual dimorphism. 



This idea of sexual dimorphism enables us to understand why castration is 

 followed by cessation of growth of horns and other structures characteristic of 

 the male, and how animals with the characteristic male features little developed 

 are essentially more feminine in their nature. 



When we come to consider colour dimorphism I think the Chairman has 

 drawn attention to an important fact which has to be kept in mind. He drew 

 Mr. Young's attention to the fact that white was a colour — indeed a combination 

 of all colours — and black is no colour. Yet the white colour of a 

 feather is essentially due to the absence of pigment, while a black feather 

 contains much pigment. A knowledge of the chemical constitution of the 

 animal pigments, I believe, will not help us much to solve the question of 

 colour differences in birds. The solution of the colour problem is more likely 

 to be found in a more intimate knowledge of the physical laws affecting colour 

 than in a knowledge of the chemical constitution of the coloured bodies. Let me 

 instance a single chemical substance which shows a distinct colour dimorphism. 

 The red iodide of mercury, when heated, is volatilised and may be condensed 

 on a glass plate as a yellow crystalline crust consisting of rhombic plates. When 

 this is rubbed or even scratched, an immediate change takes place, the rhombic 

 plates becoming broken up into octohedra while the colour at the same time 

 alters from a yellow to a brilliant scarlet. Here the chemical constitution 

 remains the same but the colour has altered on account of physical laws. 



The brilliant colours of male birds, especially that beautiful play of colours 

 often seen on their heads and necks, is probably due to microscopically minute 

 ridges and grooves on the feathers which reflect and retract the light and so 



