THE RECAPITULATION HYPOTHESIS. 309 
degree remarkable that all vertebrate animals of the most 
different classes—fishes, amphibious animals, reptiles, birds, 
and mammals—in the first periods of their embryonic 
development cannot be distinguished at all, and even much 
later, at a time when reptiles and birds are already distinctly 
different from mammals, that the dog and the man are 
almost identical? Verily, if we compare those two series of 
development with one another, and ask ourselves which of 
the two is the more wonderful, it must be confessed that 
ontogeny, or the short and quick history of development of 
the indwidual, is much more mysterious than phylogeny, or 
the long and slow history of development of the tribe. For 
one and the same grand change of form is accomplished by 
the latter in the course of many thousands of years, and by 
the former in the course of a few months. Evidently this 
most rapid and astonishing transformation of the individual 
in ontogenesis, which we can actually point out at any 
moment by direct observation, is in itself much more 
wonderful and astonishing than the corresponding, but 
much slower and gradual transformation which the long 
chain of ancestors of the same individual has gone through 
in phylogenesis. 
The two series of organic development, the ontogenesis of 
the individual and-the phylogenesis of the tribe to which 
it belongs, stand in the closest causal connection with each 
other. I have endeavoured, in the second volume of the 
“General Morphology,” * to establish this theory in detail, 
as I consider it exceedingly important. As I have there 
shown, ontogenesis, or the development of the individual, is a 
short and quick repetition (recapitulation) of phylogenesis, 
or the development of the tribe to which it belongs, determined 
