ORGANIC DIFFERENTIATION 89 



or maturation of the sexual cells, and the appearance of 

 this brilliant ornamentation is so general that there must be 

 a correlation of cause and effect ; and since the reproductive 

 cells are here the active ones, it is quite probable that either 

 they or the interstitial glands derived from them are to be 

 considered as the exciting cause of the modifications that the 

 organism presents during the period of reproduction. Pursuing 

 this line of thought, we are perhaps justified in asking if the 

 wings, new forms and brilliant colours characterizing adult 

 insects at the moment of their sexual maturity were not 

 originally their nuptial apparel. On the other hand, it might 

 be urged that the mating plumage, which in the male of some 

 birds, ruff, white heron, etc., only occurs in the courting 

 season, becomes permanent in others (cocks, pheasants, 

 peacocks, etc.) from the time when the males become adult 

 and that there are numbers of species in which the brilliant 

 adornments of the males are gradually taken on by 

 the females, as in the case of the Kingfisher family 

 and that of the small blue Butterflies of our own fields, 

 Argus or Polyommatus. This gives us a sound reason for 

 assuming that a character temporarily acquired under 

 influences peculiar to one sex, can persist when the influences 

 determining it have ceased and can subsequently, through 

 heredity, become extended to the other sex. 



Whatever be the cause or the aggregation of causes that has 

 led to a modification of an organism, for that modification to 

 be inherited it is necessary that the cause or the causes that 

 have determined it should act directly or indirectly upon the 

 germ cells. But it is also necessary that the modification the 

 reproductive cells experience be of such a nature as to react 

 in its turn upon those elements arising from them and thus, 

 by means of a series of successive releases, succeed in 

 establishing the new character. But how can this series of 

 releases be initiated with the regularity familiar to us ? If it 

 be remembered that the toxins injected into an organism 

 generally stimulate the formation of antitoxins with opposite 

 properties, we may regard it as probable that the active 

 substances contained within the ovum may be able to 

 reconstitute gradually the substances whose successive 

 modifications have caused their own formation, and thus 

 the reappearance of the characters to which they correspond. 



