INDIVIDUAL AND ANCESTRAL DEVELOPMENT 309 



in inheritance as the fertilized egg; that each cell has the constitu- 

 tion which is characteristic of the species; that it .might, under proper 

 conditions, have become a germ-cell, or any one of the various cells 

 of the body, because the substance of inheritance is transmitted 

 equally to all cells. 



According to another view, a germ-cell is the only complete and 

 independent representative of the species, since the substance of 

 inheritance is held to be contained, in its completeness, in no cells 

 except those that are predestined to produce new organisms, while 

 the ordinary tissue-cells are held to be absolutely and inevitably out 

 of the line of descent to future generations, because they contain only 

 so much of the substance of inheritance as is necessary for trans- 

 mitting the hereditary characteristics of these cells and their pre- 

 destined descendants. 



I believe that a little study of the word inheritance will show us an 

 easy way out of these paradoxes, and I do not believe I could make 

 a better use of my hour, or one that would do more to promote re- 

 search in embryology, than to point out how far the dispute is a 

 verbal one. So far as the word is used inductively, it means the 

 resemblance of child to parent, of descendants to ancestors, while 

 the difference between child and parent is called variation. These 

 words are also used, metaphorically, to designate the cause or the 

 explanation of the resemblances and differences between descendants 

 and ancestors, just as gravitation is used metaphorically to designate 

 that which makes things gravitate, and geotropism that which makes 

 roots grow downwards, and selection that which brings about sur- 

 vival in the struggle for existence. In what I have to say, I shall 

 restrict myself to the inductive meaning of these words, for I know 

 that your minds and your words are so free from the bonds of meta- 

 physics that you know we accomplish nothing by asserting that 

 heredity makes beings inherit, or that variation makes them vary, 

 or that selection selects. 



Let us, therefore, consider the word inheritance as a term to desig- 

 nate the resemblance between parent and child. You all know that 

 while the descendant does, on the average, resemble its ancestors and 

 collateral relatives more than it resembles anything else in nature, 

 it is never identical with them. We say, in our careless way, that 

 organisms exhibit specific identity behind, or in spite of, their in- 

 dividuality, when we mean that, while they resemble their parents, 

 they are different from them. This diversity in unity is true of all 

 natural objects, but it is most notable and impressive in familiar 

 living beings, in our friends and acquaintances, in our dogs and 

 horses, and in the plants that we tend with our own hands. We may 

 think of the casual stranger on the street, or the unknown citizen of 

 Timbuctoo, or the stalks in the corn-field that we pass in the train, 



