RELATIONSHIP OF SPECIES. 31 



affects fertility in so much that many species, the Pox notably, 

 fail, as a rule, to reproduce in captivity. Curious phenomena 

 such as this emphasise the great power environment has on the 

 reproductory organs, as Darwin long ago pointed out, and this 

 impresses one to take the view that environment is one of the 

 great causes of evolution. Therefore, we must bear in mind 

 that this may be the cause acting on the anomalies mentioned 

 above, and which therefore may by no means be anomalies, 

 although, to be fair, one is bound to admit that this cuts both 

 ways, and may invalidate or put out of court some of the 

 seemingly correctly graduated examples I have given in my 

 table. At the same time, one might mention that Darwin hardly 

 makes out any case for his supposition that domestication affects 

 fertility to such an extent as to cause species unfertile while wild 

 to become fertile together in their domesticated forms. 



At the time I first wrote out the above table I felt quite con- 

 fident that it was the proper thesis ; since then, however, I hope 

 I have learnt to put no very definite trust in anything. 



When we dabble in relationship between animals whose 

 common progenitor we know not, the length of whose separation 

 we know not, and whose blood affinities we know little of, we 

 cannot expect our results to be always as we should expect. It 

 might be permissible to speculate whether environment and 

 other effects, which are said to produce the separation of species 

 and cause their physical attributes to become different, can 

 cause them to come together again, so that animals once sterile 

 can once again converge and become so alike as to again breed. 

 It might be possible for the germ plasm to be so affected, how- 

 ever unlikely ; this would result in anomalies, and such pheno- 

 mena as species becoming fertile together in confinement, while 

 sterile in nature, as Darwin considered probable, but which 

 might equally well be held to be improbable. 



All the animals in Class A., term them different species, or 

 genera, or what you will, one can only, independent of struc- 

 ture, hold to be, through blood affinity, nothing more than 

 Nature's evoluting varieties, in the same way that the Cochin 

 Fowl and the Minorca Fowl are varieties, or Newfoundland and 

 Pag Dogs, and there is not much doubt that if these latter 

 (having gone through exactly the same conditions of evolution 



