II.] ON HEREDITY. 1 01 



explain the facts otherwise than by supposing the passive 

 acquisition of characters produced by the direct influence of 

 climate. 



It must be remembered, however, that my experiments, 

 which have been repeated upon several American species by 

 H. W. Edwards, with results confirmatory of my own in all 

 essential respects, were not undertaken with the object of in- 

 vestigating the question from this point of view alone. New 

 experiments, under varying conditions, will be necessary to 

 afford the true explanation of this aspect of the question; and I 

 have already begun to undertake them. 



Leaving on one side, for the moment, these doubtful, and 

 insufficiently investigated cases, we may still maintain that the 

 assumption that changes induced by external conditions in the 

 organism as a whole are communicated to the germ-cells after 

 the manner indicated in Darwin's hypothesis of pangenesis, is 

 wholly unnecessary for the explanation of these phenomena. 

 Still we cannot exclude the possibility of such a transmission 

 occasionally occurring, for, even if the greater part of the 

 effects must be attributed to natural selection, there might be 

 a smaller part in certain cases which depends on this excep- 

 tional factor. 



A complete and satisfactory refutation of such an opinion 

 cannot be brought forward at present : we can only point out 

 that such an assumption introduces new and entirely obscure 

 forces, and that innumerable cases exist in which we can 

 certainly exclude all assistance from the transmission of ac- 

 quired characters. In most cases of variation in colour we 

 have no explanation but the survival of the fittest \ and the 

 same holds good for all changes of form which cannot be 

 influenced by the will of the animal. Very numerous adapta- 

 tions, such, for instance, as occur in the eggs of animals, — the 

 markings, and appendages which conceal them from enemies, 

 the complex coverings which prevent them from drying up or 

 protect them from the injurious influence of cold, — must have 

 all arisen entirely independently of any expression of will, or of 

 any conscious or unconscious action on the part of the animals. 

 I will not mention here the case of plants, which as every one 



^ The colours which have been called forth by sexual selection must 

 also be included here. 



