64 THE GERM-PLASM THEORY 



over, was based, not merely on trie occurrence of 

 stripes in horses, which we have just discussed, 

 but on his belief.^that such stripes were common 

 in dun-coloured horses, and that there was a 

 tendency in horses to revert to dun colour. But it 

 must be confessed that the facts do not warrant 

 his conclusion. ... It is clear that stripes are at 

 least as often a concomitant of dark as of dun 

 coloured. Moreover, if Darwin's hypothesis of a 

 dun-coloured ancestor with stripes is sound, dark 

 colours such as bay and brown must be of more 

 recent origin, and accordingly there ought to be 

 a great readiness on the part of progeny of a light- 

 coloured animal when mated with a dark to revert 

 to the light. But Prof. Ewart's zebra stallion has 

 never been able to stamp his own peculiar pattern 

 or his own colours on his hybrid offspring. The 

 ground colour has been determined by the dams 

 of the hybrid." 



We have dwelt upon these points because it 

 seems to us that the very great difficulties which 

 quite obviously exist in ascertaining the exact 

 state of the case in connexion with so many of the 

 underlying facts for many other matters as to 

 which there is also grave doubt could be quoted 

 to say nothing of the difficulty of interpreting 

 them, should indicate the necessity for great 

 caution in accepting or claiming as proved, in the 

 present state of knowledge, any but a few of the 

 modern biological doctrines. 



Amongst these doctrines and theories the views 

 enunciated by Weismann, by Mendel and by de 

 Vries within recent years have attracted a very 



