GERMINAL SELECTION. 55 



the course of normal evolution. In this form they 

 appear to me to be an absolutely necessary and un- 

 avoidable inference from the facts. There must be 

 contained in the germ parts that correspond to definite 

 parts of the complete organism, that is, parts that con- 

 stitute the reason why such other parts are formed. 

 It is conceded even by my opponents that the rea- 

 son why one egg produces a chicken and another a 

 duck is not to be sought in external conditions, but lies 

 in a difference of the germinal substance. Nor can 

 they deny that a difference of germinal substance 

 must also constitute the reason why a slight hered- 

 itary difference should exist between two filial organ- 

 isms. Should there now, in a possible instance, be 

 present between them a second, a third, a fourth, or a 

 hundredth difference of hereditary character, each of 

 which could vary from the germ, then, certainly, some 

 second, third, fourth, or hundredth part of the germ 

 must have been different ; for whence, otherwise, 

 should the heredity of the differences be derived, see- 

 ing that external influences affecting the organism in 

 the course of evolution induce only non-transmissible 

 and transient deviations? But the fact that every 

 complex organism is actually composed of a very large 

 number of parts independently alterable from the 

 germ, follows not only from the comparison of allied 

 species, but also and principally from the experiments 

 long conducted by man in artificial selection, and 

 by the consequent and not infrequent change of only 

 a single part which happens to claim his interest; for 

 example, the tail-feathers of the cock, the fruit of the 

 gooseberry, the color of a single feather or group of 

 feathers, and so on. But a still more cogent proof 

 is furnished by the degeneration of parts grown use- 



