66 THE EIDDLE OF THE UNIVEKSE. 



fish-like embryo, in the form of two roundish, flat 

 bucls, the foetus is still so like that of other vertebrates 

 that it is indistinguishable from them. 



The substantial similarity in outer form and inner 

 structure which characterizes the embryo of man and 

 other vertebrates in this early stage of development is 

 an embryological fact of the first importance ; from 

 it, by the fundamental law of biogeny, we may draw 

 the most momentous conclusions. There is but one 

 explanation of it — heredity from a common parent 

 form. When we see that, at a certain stage, the 

 embryos of man and the ape, the dog and the rabbit, 

 the pig and the sheep, although recognizable as higher 

 vertebrates, cannot be distinguished from each other, 

 the fact can only be elucidated by assuming a common 

 parentage. And this explanation is strengthened 

 when we follow the subsequent divergence of these 

 embryonic forms. The nearer two animals are in 

 their bodily structure, and, therefore, in the scheme 

 of nature, so much the longer do we find their embryos 

 retain this resemblance, and so much the nearer do 

 they approach each other in the ancestral tree of their 

 respective group, so much the closer is their genetic 

 relationship. Hence it is that the embryos of man 

 and the anthropoid ape retain the resemblance much 

 later, at an advanced stage of development, when their 

 distinction from the embryos of other mammals can 

 be seen at a glance. I have illustrated this significant 

 fact by a juxtaposition of corresponding stages in the 

 development of a number of different vertebrates in 

 my Natural History of Creation and in my Anthro- 

 pogeny. 



The great phylogenetic significance of the resem- 

 blance we have described is seen, not only in the 



