216 LECTURE VIII. 



The range of divergence is as yet far from being exhausted. 

 Every one knows that children of the same parents, though 

 possessing a family likeness, are never perfectly alike, that 

 even twins or animals of the same litter still exhibit pecu- 

 liarities which enable us to distinguish them. The range may 

 be wide wdthout transgressing the limits which separate the 

 normal from the abnormal structure, and this is specially the 

 case when the parents themselves occupy the limits of the 

 normal structure. Reserving the details for another occasion, 

 I would here merely draw your attention to the fact that such 

 peculiarities may be transmitted through several generations. 

 Thus there are families in which supernumerary or webbed 

 fingers have been transmitted through several generations, 

 until frequent intermixture with normally formed individuals 

 has led to the obliteration of such abnormities. 



To characterise the family the naturahst must study all 

 these possible, deviations, and it is clear that in the absence of 

 direct observation he is liable to many errors. Natural histoiy 

 furnishes many instances of the separation of parents and 

 ofi'spriilg, young and old, male and female, until direct obser- 

 vation cleai-ly established their relationship. 



Having now arrived at the first stage, namely, the recogni- 

 tion of a certain type belonging to all individuals derived from 

 a certain stock, we must proceed further and acknowledge 

 that this type may also belong to a number of individuals, 

 which, as far as we can trace, are not descended from the self- 

 same stock. Thus, for instance^ taking into account the pre- 

 sent condition of the globe, we cannot understand how the 

 trout north of the Alps can belong to the same stock as those 

 south of the Alps, separated as they ever have been by insur- 

 mountable mountains ; or how the chamois of the Pyrenees 

 can be directly related to those of the Alps, separated as they 

 are by plains equally inaccessible to the mountain animals. 

 And yet the sum of resemblances is so great that these animals 

 might unhesitatingly be included in the same stock if their 

 descent were not known to us. We recognise a type wath 

 certain definite characters which we term species, and which 

 we might define as follow : — all individuals possessing such 



