330 Mr. P. R. Lowe on Coloration as a Factor in 



recently upheaved so as to form the Peruvian and Columbian 

 Andes, the Cordilleras of Venezuela, the Central American 

 mountain ridge, and the interrupted rock -systems of the 

 Greater Antillean islands. The rock-systems of the whole 

 of this green area are, for all practical purposes, in almost 

 complete geological continuity and, as compared with the 

 rock-systems represented by the red area, are things of 

 yesterday. 



Now, I think it is pretty safe to conclude that the original 

 centre of distribution of the genus Coereba was represented 

 by this red-coloured Brazilian land-mass. This seems indi- 

 cated by the more generalised, more constant, and less 

 differentiated nature of tlie colouring and colour-pattern of 

 the race without white wing-spots. But assuming that the old 

 Brazilian land-mass did indeed represent the original centre 

 of distribution of the genus, we find that no sooner did the 

 genus extend its area of distribution to the more recent 

 land-areas, coloured green, than this factor of the white 

 wing-spot became conspicuous and absolutely constant in the 

 new area of occupation. It looks, indeed, as if the poten- 

 tiality of the germ-cell, in the original and older race, to 

 produce the white wing-spot had been held in check in the 

 old area of distribution, but that the moment migration to a 

 new and isolated area took place, this tendency of the germ- 

 cell was unchecked or given free play. That there was a 

 potentiality in this direction always resident in the germ- 

 cell is, I think, indicated by the fact that every now and 

 then, but still only in quite rare instances, indications of a 

 white wing-spot crop up in the race without white wing- 

 spots. In a large series of 70 specimens, for example, from 

 Matto Grosso, Mr. Allen found a very small percentage. 



It may be thought that this is a very long story about 

 a very small thing ; because, as anyone can see by examining 

 these Coereba specimens, the presence or absence of a white 

 wing-spot in the two respective races seems a very trivial 

 and almost contemptible circumstance. But it is just for 

 this very reason of apparent triviality that I have used 

 it as an example. For the point is this — could anyone 



