22 INHERITANCE. Chap. XIII. 



purely- bred animals or plants reassiime long-lost characters,— 

 when the common ass, for instance, is born with striped legs, 

 when a pure race of black or white pigeons throAvs a slaty- 

 blue bird, or when a cultivated heartsease with large and 

 rounded flowers produces a seedling with small and elongated 

 flowers, — we are quite unable to assign any proximate cause. 

 When animals run wild, the tendency to reversion, which, 

 though it has been greatly exaggerated, no doubt exists, is 

 sometimes to a certain extent intelligible. Thus, with feral 

 pigs, exposure to the weather will probably favour the growth 

 of the bristles, as is known to be the case with the hair of 

 other domesticated animals, and through correlation the tusks 

 will tend to be redeveloped. But the reappearance of coloured 

 longitudinal stripes on j^oung feral pigs cannot be attributed 

 to the direct action of external conditions. In this case, and 

 in many others, we can only say that any change in the 

 habits of life apjoarently favour a tendency, inherent or latent 

 in the species, to return to the primitive state. 



It will be shown in a future chapter that the position of 

 flowers on the summit of the axis, and the position of seeds 

 within the capsule, sometimes determine a tendency towards 

 reversion ; and this apparently depends on the amount of sap 

 or nutriment which the flower-buds and seeds receive. The 

 position, also, of buds, either on branches or on roots, some- 

 times determines, as was formerl}^ shown, the transmission of 

 the character proper to the variet}^, or its reversion to a former 

 state. 



We have seen in the last section that when two races or 

 species are crossed there is the strongest tendency to the re- 

 appearance in the offspring of long-lost characters, possessed 

 by neither parent nor immediate progenitor. When two 

 white, or red, or black j)igeons, of well-established breeds, 

 are united, the ofispring are almost sure to inherit the same 

 colours ; but when differently-coloured bii ds are crossed, the 

 opposed forces of inheritance apparently counteract each 

 other, and the tendency which is inherent in both parents to 

 produce slaty-blue offspring becomes predominant. So it is 

 in several other cases. But when, for instance, the ass is 

 crossed with E. indicus or with the horse,— animals which 



