626 HISTORY OF GEOLOGY. 



and others, for the history of the discussion, and for 

 the grounds of the decision ; and I shall quote very 

 briefly the main points and conclusions to which the 

 inquiry has led 5 . 



It may be considered, then, as determined by 

 the over-balance of physiological authority, that 

 there is a capacity in all species to accommodate 

 themselves, to a certain extent, to a change of ex- 

 ternal circumstances ; this extent varying greatly 

 according to the species. There may thus arise 

 changes of appearance or structure, and some of 

 these changes are transmissible to the offspring: but 

 the mutations thus superinduced are governed by 

 constant laws, and confined within certain limits. 

 Indefinite divergence from the original type is not 

 possible ; and the extreme limit of possible varia- 

 tion may usually be reached in a brief period of 

 time : 'in short, species have a real existence in 

 nature, and a transmutation from one to another 

 does not exist. 



Thus, for example. Cuvier remarks, that not- 

 withstanding all the differences of size, appearance, 

 and habits, which we find in the dogs of various 

 races and countries, and though we have (in the 

 Egyptian mummies) skeletons of this animal as it 

 existed three thousand years ago, the relation of the 

 bones to each other remains essentially the same ; 

 and, with all the varieties of their shape 15 and size, 



5 Lyell, B. iii. c.. iv. 



6 Ossem. FOM. Disc. Prel. p. 61. 



