42 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol. XVI 



nearest to the seats of excessive vitality, i.e., the head, lungs, and caudal regions. 

 But this does not answer the question why." 



I was not aware that the head and lungs and tail were endowed with excessive 

 vitality. As I have already remarked, the katabolic stimulus of the male 

 generative cells on the vegetative cells is the fundamental cause of sexual 

 dimorphism. The energy which results from this stimulus may reveal itself in 

 excessive bodily or nervous activity or in brilliancy of colour. But while in 

 this way energy is set free it is never wasted, it is conserved, and I believe 

 always conserved to some useful purpose. To every action there is an equal 

 and opposite reaction. The reaction checks waste and diverts the energy into 

 useful channels. Hence it comes about that in opposition to the katabolic 

 tendencies of the male, other subsidiary laws are called into play, e. g., the law 

 which maintains that useless structures and organs disappear and atrophy while 

 useful structures and functions are developed. But even this law is limited by 

 other laws which check too great specialism. The brain of man for example 

 is a most useful organ, and it would be theoretically advantageous to develop it 

 to a maximum extent, but other factors prevent this specialising. Without a 

 well-developed body the brain becomes useless. Mens sana in corpore sano 

 is eminently true. A tool without the hand to work it is no good. One law 

 reacts against another law so that extremes are prevented. It would be quite 

 impossible for me at present to consider the many laws that are thus called into 

 play. I cannot believe that the four tendencies as Mr. Young has called them, 

 suffice to explain the facts. The fundamental reason for sexual dimorphism 

 lies in the fact that the male has katabolic tendencies while the female has 

 anabolic proclivities, and these tendencies are prevented from developing into 

 extremes by the operation of many other laws, the laws so called into play 

 differ in individual instances; a knowledge of these laws will answer Mr. Young's 

 question why ? The answer will not be the same in every case, and it can only 

 be made by a special study of individual groups, such as Mr. Dewar has at 

 present attempted in the case of birds. 



Wm. GLEN LISTON, M.D., F.R.S.E,, Captain, I.M.S. 



REPLY TO CAPTAIN LISTON. 

 By L. C. H. Young. 



I cannot avoid making some reply to Captain Liston because he seems to 

 have misunderstood in some respects the drift of my remarks. 



In the first place as to the definition of " sexual dimorphism," I did r.ot 

 intend to make any definition but merely to explain in an untechnical manner 

 that discussions on sexual dimorphism were generally confined to the explanation 

 of what naturalists term " secondary sexual characters, "and these are certainly 

 the only ones which Darwin and Wallace discuss. 



If we include in it those differences which must exist in every species as being 

 essential to the sexual relation we are getting outside the subject discussed in 

 Mr, Dewar's paper altogether. 



