2 8 EX VI RIB US VIVIMUS. 



from common experience as to ageing, and some 

 facts bearing on it which it is needless to parti- 

 cularize are given in the ' Statements as to Longevity,' 

 below. 



What we are then endeavouring to exaniine in 

 various species of lower animals and in man, viz. 

 normal potential longevity, varies in accordance with 

 two sets of influences, the external agencies or spe- 

 cific 'milieu,' acting directly on individuals, and an 

 inherent limiting agency. To the first, all organisms 

 are severally subject ; the second seems to possess 

 a very small power in some. Both these are here- 

 ditary influences, as is implied in their truly specific 

 character ; the inherent is so by hypothesis, the ex- 

 ternal agencies are less obviously so, being indirectly 

 inherited by the transmission of structural capacities 

 and necessities involving the same details of life in the 

 offspring as in the parent, 



Not less hereditary is that average longevity which 

 was spoken of as constituting the study known as 

 ' mortality.' It, equally with potential longevity, is a 

 specific character as truly as a tuft of feathers or an 

 additional antennary joint, and is determined by the 

 reciprocal relations of the ' environment ' and the 

 'organism,' and with a constant orgaftism it cannot 

 vary, whilst, if the ' environment ' is not constant, the 

 organism must become a new species on the evolu- 

 tion hypothesis, or cease to exist on the special-^ 

 creation hypothesis being no longer fitted to its 



