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 
