

462 



EXTINCTION OF SPECIES. 



LCii. XLII. 



We liave only to reflect on the causes of extinction enume- 

 rated in this chapter, and we at once foresee the time when 

 even in these genera so many gaps will occur, so many tran- 

 sitional forms will be lost, that there will no longer be any 

 difficulty in assigning definite limits to each species. The 



fe) 



'm 



other^ must be an exception to the general rule, wlietlier 

 in our own times or at any period of the past, because the 



ms 



for a long succession of antecedent periods to those powerful 

 causes of extinction which are slowly, but incessantly, at 

 work in the organic and inorganic worlds. 



Dr, Hooker, in commenting on the loss of a hundred species 

 of plants in the course of the last three and a half centuries 

 in St. Helena,^ remarks, ^ every one of these species was a 

 link in the chain of created beings, which contained within 

 itself evidence of the affinities of other species both living 

 and extinct, but which evidence is now irrecoverably lost.' 



It is affirmed by Darwin that genera which in the present 

 state of the globe are most dominant contain also the most 

 variable species. It is in such genera that the 



formation 



most 



more 



species are fast dying out ; and that such has always been the 

 order of Nature is proved by the fact, that while certain forms 

 are characteristic of every geological period, these same are 

 unknown or feebly represented, whether in older strata or 

 in formations of later date. 



ima 



true we ought to discover in a fossil state all the intermediate 



dissimilar 



connected 



must 



NatuT 



tacitly assume that it is part of 



animal 



Yet these 



same 



objectors to the theory would hardly expect that the 

 species of plants just alluded to as having been so recently 



Hele 



left memorials of 



^ See above, p. 453. 



^ 



J 



\ 



