INDIVIDUAL AND ANCESTRAL DEVELOPMENT 313 



an epigenetic explanation of the specific constitution with which the 

 germ begins its development, I do not see how we can account for the 

 facts of individual development from the standpoint of epigenesis. 



The hypothesis we have been considering has much to commend 

 it, and it is, no doubt, a step in the right direction. Inasmuch as it 

 emphasizes the familiar truth, so often forgotten by speculative zoo- 

 logists, that a living being is no metaphysical abstraction, no self- 

 sustaining, self-sufficient entity, no thing in itself, but a natural body 

 in a natural world, of which it is a part, and with which it is in continual 

 reciprocal interaction, so far as it carries our vagrant minds back 

 from metaphysics to this great scientific truth, it seems to me to 

 be altogether good; for the amount of idle speculation which has 

 sprung from neglect of this truth is appalling. I ask your attention 

 to it because I shall have more to say about it. It has been a familiar 

 thought with me for nearly thirty years, not because of any original- 

 ity of my own, but because I learned it from the study of the Origin 

 of Species. I have lost sight of it now and then, amid the paradoxes 

 and perplexities of speculative biology, but I have found them to 

 vanish like mist before the wind so soon as I recalled it; so I ask you 

 to bear in mind, at least for the rest of my hour, that a living being 

 is no self-sufficient whole, but a natural body which is part of a 

 natural world, and that this truth is no metaphysical subtilty, but 

 a fact. 



So far as it insists upon, and is based upon, this important truth, 

 the hypothesis we have been considering seems to me to be sound 

 and valuable. Inasmuch as it fails to consider the truth that indi- 

 vidual development is a preparation for the struggle of life, it seems 

 to me to be only a partial and imperfect account of individual de- 

 velopment. 



It is not the only view that has advocates. You know what a prom- 

 inent place in literature the doctrine of germ-plasm has held. Accord- 

 ing to this doctrine, individual development is the unfolding of the 

 organization that preexists in the germ. With qualifications which 

 need not detain us, it is the doctrine that the species resides, in its 

 completeness, in no cells except germ-cells, and that differentiation 

 is due to the differential distribution of the substance of inheritance, 

 each cell being held to receive only so much of this substance as bears 

 its hereditary qualities and those of its predestined descendants. So 

 far as it deals with individual development, its essential feature is the 

 definitiveness of cell-division, for it is based upn the opinion that the 

 ordinary tissue-cells are utterly and completely cut off from posterity 

 because no cell except a germ-cell contains all the hereditary qualities 

 of the species. 



I shall not discuss this doctrine in detail, because it seems to me to 

 arise from neglect of the truth that neither a germ-cell nor any other 



