258 THE INDUCTIONS OF BIOLOGY. 



have lost their horns. At one time, there existed in Scot- 

 land a race of pigs with solid feet instead of cleft feet. In 

 pigeons, according to Mr Darwin, " the number of the cau- 

 dal and sacral vertebra vary ; as does the number of the 

 ribs, together with their relative breadth and the presence of 

 processes." 



That variations both small and large which arise without 

 any specific assignable cause, tend to become hereditary, was 

 shown in the last chapter. Indeed the evidence which proves 

 Heredity in its smaller manifestations, is the same evidence 

 which proves Yariation ; since it is only when there occur vari- 

 ations, that the inheritance of anything beyond the structural 

 peculiarities of the species, can be proved. It remains here, 

 however, to be observed, that the transmission of variations 

 is itself variable ; and that it varies both in the direction of 

 decrease and in the direction of increase. An individual trait 

 of one parent, may be so counteracted by the influence of the 

 other parent, that it may not appear in the offspring ; or not 

 being so counteracted, the offspring may possess it, perhaps 

 in an equal degree or perhaps in a less degree ; or the off- 

 spring may exhibit the trait in even a still higher degree. 

 Of the illustrations of this, one must suffice. I quote it from 

 the essay by Dr Struthers, referred to in the last chapter. 



"The great-great-grandmother, Esther P — — (who mar- 

 ried A L ), had a sixth little finger on one hand. Of 



their eighteen children (twelve daughters and six sons), only 

 one (Charles) is known to have had digital variety. We 

 have the history of the descendants of three of the sons, 

 Andrew, Charles, and James. 



" (1.) Andrew L had two sons, Thomas and Andrew; 



and Thomas had two sons all without digital variety. Here 

 we have three successive generations without the variety 

 possessed by the great-grandmother showing itself. 



"(2.) James L , who was normal, had two sons and 



seven daughters, also normal. One of the daughters became 

 Mrs J (one of the informants), and had three daughters 



