312 EMBRYOLOGY 



velopmental changes in one part of the body and similar changes in 

 other parts, although this is, no doubt, an important factor in all 

 development. Other well-known facts, such as the development of 

 a bud into a leaf-shoot under certain conditions, and into a flower- 

 shoot under others, lend support to the doctrine that there is a cor- 

 relation between the history of each cell and its interactions with 

 other cells, but the doctrine that cell-division is always division into 

 like parts, and that it is the internal environment of each cell that 

 calls out one of its possibilities and leaves the others latent, is not 

 in itself an answer to the question why, as the egg develops into 

 ar> embryo, its cells find themselves in a little world of their own 

 making, which is so much like that in which their ancestors developed 

 that the end-product is an individual fitted for the normal life of its 

 kind. 



This seems to me to be the real problem of embryology. The ex- 

 ternal world of a hen's egg in an incubator is the same as that of the 

 duck's egg beside it. So far as the duckling and the chick owe their 

 fitness for the world into which they are to be born to mechanical condi- 

 tions, they must owe it to conditions which they find within the egg, or 

 make there for themselves, through their own activity as living beings. 

 So far as the nutritive and chemical changes that go on in the hen's 

 egg, the effects of gravity and pressure, of the interaction of cell and 

 cell, of organ and organ, are more like those under which ancestral 

 hens developed than they are like those under which ancestral ducks 

 developed, this must be due to a characteristic difference between 

 the interactions of a chick and those of a duck. While it is, no doubt, 

 in the interaction between the living organism and the world around 

 it that life consists, this does not, in itself, tell us why the internal 

 environment of the cells of the developing chick is so much like that 

 of ancestral embryos that the end-product is fitted for the life of 

 fowls. 



The hypothesis we are considering is inadequate in so far as it fails 

 to consider the truth that the development of the chick, or that of 

 the human infant, or that of any other organism, is a preparation for 

 a test that is to come later, in the struggle of life: since the most 

 significant fact in the reciprocal interaction between the developing 

 organism and its -environment is that it is a preparation for its inter- 

 action, at a later period, with an environment of competitors and 

 enemies. So far as the origin of an individual organism, fitted for the 

 state of life into which it is to be born, is in question, the orderly 

 unfolding, by the interaction between a germ and its internal environ- 

 ment, of all the stages which made up the ancestral environment for 

 epigenetic development, in due succession and order, seems to be more 

 like evolution than epigenesis, unless, indeed, there is something in 

 this interaction which we have not yet considered. Unless we can find 





