278 AKIMAL COLORATION. 



possible, ,nearlT always produced female butterflies ; on the 

 other hand, by cutting short the food supplies a preponderance 

 of males were hatched. Similar experiments were made with 

 the Camberwell Beauty and a moth. Dr. C. V. Riley made a 

 larger number of experiments, which did not appear to him 

 to be quite so conclusive as to the direct influence of food ; but 

 he admitted that "there is a certain relation between organic 

 vigour and sex, and that the latter may be determined in the 

 offspring, by the amount of vigour or vitality — creative or 

 organic force — in the parents, and that the female is in some 

 way connected with increased, and the male with lessened, 

 vitality." This question, however, is not one which can be 

 treated of in the present volume ; the reader is referred to 

 Messrs. Geddes and Thomson's work " The Origin of Sex " for 

 further details : all that I desire to point out is that Mr. 

 Stolzmann's conclusions are, on the whole, borne out by ex- 

 periments. 



Now, seeing that upon the females devolve the chief cares 

 of nest building — at least in the majority of species — it is not 

 surprising that the greater number of eggs laid should be 

 badly nourished : the bird has less opportunity of looking 

 after her own comfort ; and on the other hand, if we may 

 suppose that the active males will tend to reproduce in their 

 ofl^spring a preponderance of males, if they themselves, as will 

 probably be the case, are in a better condition than the females 

 with whom they pair. This statement, I should observe, is M. 

 Stolzmann's. In any case there is clearly evidence tending 

 to show that the percentage of male births among birds is 

 greater than that of females. 



Now, the preponderance of males over females is not advan- 

 tageous to the species. And natural selection, as M. Stolzmann 

 points out, is less concerned with the well-being of the 



