12 Darbishire, Mendelian Principles of Heredity. 



the neighbourhood ; but even if the smaller trunk were 

 lucky enough to find such an one its offspring would be 

 less trunked even than itself! If the original trunked 

 variety paired with a trunkless relative the swamping 

 would be ever so much faster : but I leave the reader to 

 pursue this argumentation for himself, suffice it to say 

 that these trunk-bearing sports would on this view be 

 very soon wiped out. 



But if we adopt the conceptions of gametic purity 

 and unit-characters, there is no reason, when once the 

 variation has arisen, why it should not be perpetuated. 

 For its germ-cells represent trunk-bearing elephants ; if it 

 mated with a similar beast its offspring would all be 

 trunk-bearing and in the same degree ; if on the other 

 hand it met a trunkless form, the result of such a union, 

 the hybrid in other words, would have a trunk if the 

 possession of that organ were dominant, and would not if 

 it were recessive; but whichever of these was the case, 

 25 % of the next generation would be true-breeding trunk- 

 bearers ; and so on. This illustration may be crude, but 

 I hope it shows the kind of way in which, according 

 to these new conceptions, such a variation might be 

 perpetuated ; while according to the biometric view of 

 heredity this would not be the case. 



We have seen that a single unit-character continues 

 to produce its like so long as it unites with its like until a 

 new variation arises from it ; but, when we come to con- 

 sider [c) Compound characters, we find that new characters 

 can arise in another way than by a discontinuous variation. 

 I will take an example with which I am familiar. When 

 a yellow-and-white Japanese waltzing mouse is crossed 

 with an albino, a hybrid is produced which is unlike 

 either parent, being, with some exceptions, hardly 

 distinguishable from the common house-mouse {see 



