116 THE GENEALOGY OF ANIMALS iv 



given direction, but they permit and favour a 

 tendency in that direction which already exists. 



It is true that, in the long run, the origin of 

 the organic molecules themselves, and of their 

 tendencies, is to be sought in the external world ; 

 but if we carry our inquiries as far back as this, 

 the distinction between internal and external 

 impulses vanishes. On the other hand, if we 

 confine ourselves to the consideration of a single 

 organism, I think it must be admitted that the 

 existence of an internal metamorphic tendency 

 must be as distinctly recognised as that of an 

 internal conservative tendency ; and that the 

 influence of conditions is mainly, if not wholly, 

 the result of the extent to which they favour the 

 one, or the other, of these tendencies. 



III. There is only one point upon which I 

 fundamentally and entirely disagree with Professor 

 Haeckel, but that is the very important one of 

 his conception of geological time, and of the 

 meaning of the stratified rocks as records and 

 indications of that time. Conceiving that the 

 stratified rocks of an epoch indicate a period of 

 depression, and that the intervals between the 

 epochs correspond with periods of elevation of 

 which we have no record, he intercalates between 

 the different epochs, or periods, intervals which he 

 terms "Ante-periods." Thus, instead of con- 

 sidering the Triassic, Jurassic, Cretaceous, and 

 Eocene periods, as continuously successive, he 



