794 ANATOMY OF VERTEBRATES. 



the more concentratively simplified and specialised foot of the 

 Horse. 1 



Rhinoceroses and Zebras, however, tread together the arid 

 plains of Africa in the present day : and the Horse has multiplied 

 in that half of America where two or more kinds of Tapir still 

 exist. That the continents of the eocene or miocene periods were 

 less diversified in respect of swamp and sward, pampas or desert, 

 than those of the pliocene period, has no support from observa- 

 tion or analogy. 



Assuming, then, that Palceotherium did ultimately become 

 Equus, I gain no conception of the operation of the effective 

 force by personifying as f Nature ' the aggregate of beings which 

 compose the universe, or the laws which govern these beings, by 

 giving to my personification an attribute which can properly be 

 predicated only of intelligence, and by saying, e Nature has se- 

 lected the mid-hoof and rejected the others.' 



As some paragraphs in my ' Preface ' have been misconceived, 2 

 I must further observe, to put my meaning beyond doubt, that, 

 to say that Pal&otlierium has graduated into Equus by ' Natural 

 Selection ' is an explanation of the process of the same kind and 

 value as that which has been proffered of the mystery of ' secre- 

 tion.' For example, a particular mass of matter in a living 

 animal takes certain elements out of the blood and rejects them 

 as f bile.' Attributes were given to the liver which can only be 

 predicated of the whole animal : the ' appetency ' of the liver, it 

 was said, was for the elements of bile, and ' biliosity ' or the 

 * hepatic sensation ' guided the gland to their selection. 3 



Such figurative language, I need not say, explains absolutely 

 nothing of the nature of bilification. One's surprise is that 

 6 tropes ' and ( personified acts ' should not have died out, as ex- 

 planatory devices, with the ( archeus faber,' the l nisus formativus,' 

 and other self-deceiving, world- beguiling simulacra of science, 

 with the last century ; and that a resuscitation should have had 

 any success in the present. It is of interest as illustrating the 

 6 alternation of generations.' 



What, then, are the facts on which any reasonable or intelli- 

 gible conception may be formed of the mode of operation of the 



1 xvn'. p. 397. 



2 Referring to my ' Anatomy of Vertebrates,' in the fourth edition of the ' Origin of 

 Species by Natural Selection,' &c, the author asserts that 'he' (Professor Owen) ' at 

 the same time admits that Natural Selection may have done something towards this 

 end.' Mr. Darwin does not quote the passage or refer to the page on which he 

 founds his assertion. — ccxm" (1866), Histor. Pref. p. xviii. 



3 cccxxviii". vol. i. p. 268, and passim. 



