Embryology. 101 
chapter on Classification—we have seen that if each 
species were created separately, no reason can be 
assigned why they should all have been turned out 
upon structural patterns so strongly suggestive of 
hereditary descent with gradual modifications, or slow 
divergence—the result being group subordinated to 
group, with the most generalized (or least developed) 
forms at the bottom, and the highest products of 
organization at the top. And now we see—or shall 
immediately see—that this consideration admits of 
being greatly fortified by a study of the develop- 
mental history of every individual organism. If it 
would be an unaccountable fact that every separately 
created species should have been created with close 
structural resemblances to a certain limited number 
of other species, less close resemblances to certain 
further species, and so backwards ; assuredly it would 
be a still more unaccountable fact that every indi- 
vidual of every species should exhibit in its own 
person a history of developmental change, every term 
of which corresponds with the structural peculiarities 
of its now extinct predecessors—and this in the exact 
historical order of their succession in geological time. 
The more that we think about this antithesis between 
the naturalistic and the non-naturalistic interpreta- 
tions, the greater must we feel the contrast in respect 
of rationality to become; and, therefore, I need not 
spend time by saying anything further upon the 
antecedent standing of the two theories in this 
respect. The evidence, then, which I am about to 
adduce from the study of development in the life- 
histories of individual organisms, will be regarded by 
me as so much unquestionable evidence in favour of 
