252 THE ZOOLOGIST. 



What is to prevent an evolution of this Onager-like type, 

 under the influence of the same evolutionary duction that has 

 been acting on the striped Zebra line, to specialize into E. asinus ? 



Condition 1 to be a physiological state, in which this condition 

 is so congenial to the germ plasm of nearly related forms 

 passing through it, that they, while under its influence, would 

 so retain their relationship and germ plasm affinity that fertile 

 hybrids would be produced between them. 



Condition 2 is a physiological state after the evolution of 

 these forms from Condition 1. One inducing a physiological 

 condition congenial and necessary, let us say, to rock-haunting 

 species, and one causing them to become infertile with the 

 ancestral types left behind in a different physiological environ- 

 ment. These specialized (?) forms resuming their congeniality 

 inter se, and again producing fertile young on their arrival at 

 Condition 2, and after their passage through the evolutionary 

 period (congeneric barrier). 



We now arrive at the result that, speaking congenially (or 

 even specifically or generically), E. zebra is nearly akin to 

 E. asinus, and remote from the ancestral types, although 

 retaining the Zebra markings characteristic of this type ; and in 

 so much this would meet facts similar to those put forward by 

 Mr. Pocock. 



I have said in the above sentence " even specifically or 

 generically " we have admitted we cannot separate the " a " 

 Zebra strain from the "/3 " strain, notwithstanding that they do 

 not connect genealogically except through the ancestral Quagga- 

 like type, then why should we disconnect E. asinus from them ? 

 Are we to separate the E. asinus type on account of a different 

 coloration from the Zebra type, and classify it with E. onager, 

 while we associate the "a" and "/3" Zebra strains in one 

 species, although they (the latter) are practically almost as 

 distinct from each other as from the asinus strain ? Is E. asinus 

 to be taken from the evolutionary condition No. 2 and classed 

 with animals of the evolutionary condition No. 1, when it has 

 arrived at the same stage in evolution similar and congenial to 

 the E. zebra strains? 



I do not wish to imply here, by using the species I have in 

 this illustration, that these Equines have been subjected to or 



