v.] IN THE THEORY OF NATURAL SELECTION. ^2^ 



the supposition that acquired molecular states of certain groups 

 of cells can be transmitted to the offspring. This supposition 

 could only be rendered intelligible by some theory of prefor- 

 ynation \ such as Darwin's pangenesis ; for the latter theory 

 certainly belongs to this category. We must assume that each 

 single part of the body at each developmental stage is, from 

 the first, represented in the germ-cell as distinct particles of 

 matter, which will reproduce each part of the body at its 

 appropriate stage as their turn for development arrives. 



I will only briefly indicate some of the inevitable con- 

 tradictions in which we are involved by such a theor}^ One 

 and the same part of the body must be represented in the 

 germ- or sperm-cell by many groups of gemmules, each group 

 corresponding to a different stage of development ; for if each 

 part gives off gemmules, which ultimately reproduce the part 

 in the offspring, it is clear that special gemmules must be given 

 off for each stage in the development of the part, in order to 

 reproduce that identical stage. And Darwin quite logically 

 accepts this conclusion in his provisional hypothesis of pan- 

 genesis. But the ontogeny of each part is in reahty continuous, 

 and is not composed of distinct and separate stages. We 

 imagine these stages as existing in the continuous course of 

 ontogeny ; for here, as in all departments of nature, we make 

 artificial divisions in order to render possible a general con- 

 ception, and to gain fixed points in the continuous changes of 

 form which have in reality occurred. Just as we distinguish 

 a sequence of species in the course of phylogeny, although 

 only a gradual transition, not traversed by sharp lines of 

 demarcation, has taken place, so also we speak of the stages 



^ It is generally known that the earlier physiologists believed in what 

 was called the ' evolutionary theory,' or the ' theory of preformation.' 

 This assumes that the germ contains, in a minute form, the whole of the 

 fully-developed animal. All the parts of the adult are preformed in the 

 germ, and development only consists in the growth of these parts and 

 their more perfect arrangement. This theory was generally accepted 

 until the middle of the last century, when Kaspar Friedrich VVolif 

 brought forward the theory of ' epigenesis,' which since that time has 

 been the dominant one. This assumes that no special parts of the germ 

 are preformations of certain parts of the fully-developed animal, and that 

 these latter arise by a series of changes in the germ, which gradually 

 gives rise to them. In modern times the theory of preformation has 

 been revived in a less crude form, as is shown by the ideas of Nageli, 

 and by Darwin's 'pangenesis.' — A. W., 1888. 



