21 



female is the more important of the two. The female is the 

 guardian of the future brood, and her destruction at any time 

 before her eggs are properly disposed of with a view to the welfare 

 of the next generation, means depriving that next generation of a 

 large mass of recruits. When the eggs are once laid, the after-care 

 of the family does not concern the butterfly as it does the bird, but 

 still the eggs are carried by the butterfly for a sufficiently long 

 period before laying to make it highly necessary to run as few risks 

 as may be. Hence, I think, the special provisions for guarding the 

 life of the female. The safety of the female is called for in the 

 interest of the race. 



It seems to be the case, as we have already noticed, that females 

 generally have a greater tendency to vary than their corresponding 

 males. " Varium et mutabile semper Femina " has a wider applica- 

 tion than was originally intended. This fact, as has been pointed 

 out by Professor Poulton, has no doubt contributed to the bringing 

 about of the phenomena with which we have just now had to deal. 

 In the diversity of material presented for operation by the compara- 

 tive instability of the female sex, Natural Selection has found its 

 opportunity for specially safeguarding the interests of that sex, and 

 through it those of the race at large. 



We may claim then to have found a basis of utility for many of 

 the manifestations of sexual dimorphism which have presented 

 themselves to our notice. It must nevertheless be admitted that 

 our present knowledge does not permit us to assign such a signifi- 

 cance to every cafe that exists. We must be content for the 

 present to acknowledge that there are certain features associated, if 

 we may use the expression, with femaleness ; beyond which 

 recognition we cannot go. This is the case, for example, with dark 

 spots on the wings which characterise the females of our common 

 whites. 



One more question may be asked and answered in conclusion. 

 What bearing have the facts of seasonal dimorphism, discussed in 

 my former lecture, on the sexual dimorphism which has been our 

 subject to-day ? We have obtained some insight into the principles 

 which underlie the two sets of phenomena considered separately ; 

 what results are found to follow from the two in combination ? 

 The answer is an interesting one ; but in order to arrive at its full 

 value, it will be necessary to recall some of the conclusions arrived 

 at on the former occasion. It will be remembered that we found 

 reason for thinking that in tropical regions the dry season was a 

 time of greater stress and competition than the wet ; and that the 

 method of concealment was probably a more efficient means of 

 protection than the method of display. In accordance with this 

 we found that many species which alternated between a cryptic and 

 an aposematic or " warning " coloration, reserved the former, being 

 the more efficacious mode, for the period of drought. In view of 

 the facts adduced during the present lecture, it is interesting to 



