According to Weismann's conception, 'every part of the body of the ant' (_loc. cit._, p. 326) 'that is differently formed in the males, females, and workers is represented in the germplasm by three (sometimes four) corresponding determinants; but on the development of an egg never more than one of these attains to value--_i.e._, gives rise to the part of the body that is represented--and the others remain inactive.' This structure of the germplasm Weismann attributes to the operation of selection. 'For in the ant state' (_loc. cit._, p. 326) 'the barren individuals or organs are metamorphosed only by the selection of the germplasm, from which the whole state proceeds. In respect of selection, the whole state behaves as a single animal. The state is selected, not the single individuals, and the various forms behave exactly like the parts of one individual in the course of ordinary selection.' Naturally, from the views on the germplasm theory and on the doctrine of determinants that I have expressed in this book, I cannot accept the explanation Weismann thus gives of the facts. It is true that Weismann holds his own explanation to be the only conceivable explanation. 'For there are only two possible _a priori_ explanations of adaptations for the naturalist, namely, the transmission of functional variations and natural selection' (_loc. cit._, p. 336); 'but as the first of these can be excluded' (on account of the infertility of workers and soldiers), 'only the second remains.' But are the alternatives really only as Weismann suggests? Is there no choice left for the naturalist? When I was reading his _All-sufficiency of Natural Selection_, kindly sent me by the author, it came into my mind that I could not accept his dilemma. For the different individuals in the insect states may be explained in a third way--in a way overlooked by Weismann. This third explanation is nothing more than the subject of all this treatise of mine. It is that, in obedience to different external influences, the same rudiments may give rise to different adult structures. I am glad that the same answer has been made to Weismann's _All-sufficiency of Natural Selection_ by two biologists, Herbert Spencer and Emery, simultaneously with mine. Emery, a specialist upon the structure of ants, and Herbert Spencer, relying upon the investigations of several Englishmen, have sought to prove that the differences between the individuals in the colonies of ants, bees, and termites, have been slowly called into existence by the operation of external influences affecting the egg in its situation and food during development.