ON VARIATIONS. 355 



dogs is well known. Hounds seem to degenerate most 

 rapidly of all, whilst greyhounds and pointers also de- 

 cline rapidly. Darwin * was informed by Dr. Falconer 

 that bull-dogs " not only fall off after two or three 

 generations in pluck and ferocity, but lose the under- 

 hung character of their lower jaws; their muzzles be- 

 come finer and their bodies lighter." He also men- 

 tions a case of a pair of setters, born in India, which 

 perfectly resembled their Scotch parents. Several 

 litters were raised from them in Delhi, but none of the 

 young dogs obtained resembled their parents in size or 

 make, their nostrils being more contracted, their noses 

 more pointed, their limbs more slender, and their size 

 inferior. On the coast of Guinea, " dogs, according to 

 Bosnian, alter strangely; their ears grow long and stiff 

 like those of foxes, to which colour they also incline, 

 so that in three or four years they degenerate into very 

 ugly creatures; and in three or four broods their bark- 

 ing turns into a howl." 



Darwin considers this tendency to rapid deteriora- 

 tion in European dogs may be largely attributed to re- 

 version. It is of course possible that this may be the 

 case, but it seems to me more probable that it is due to 

 the direct and cumulative effects of changed conditions 

 of life. 



The cumulative effect of conditions of life is ad- 

 mitted, even by Weismann, in the case of the butterfly 

 Polyommatus plilccas. As already mentioned in Chap- 

 ter VII., this occurs as a reddish gold variety in Ger- 

 many and other countries of similar latitude, and as a 

 much darker variety in more southerly countries, as 



*IMd.,i. p. 39. 



