TEEOR Y OF NA TUBAL SELECTION. 24 V 



unailiocted, and serves as a record of the past condition of 

 the species. Hence it is that existing species during the 

 early stages of their development so often resemble ancient 

 and extinct forms belonging to the same class. On this 

 view of the meaning of erabryological resemblances, and 

 indeed on any view, it is incredible that an animal 

 should have undergone such momentous and abrupt trans- 

 formations as those above indicated, and yet should not 

 bear even a trace in its embryonic condition of any sudden 

 modification, every detail in its structure being developed 

 by insensibly fine steps. 



He who believes that some ancient form was transformed 

 suddenly through an internal force or tendency into, for 

 instance, one furnished with wings, will be almost com- 

 pelled to assume, in opposition to all analogy, that many 

 individuals varied simultaneouslv. It cannot be denied 

 that such abrupt and great changes of structure are widely 

 different from those which most species apparently have 

 undergone. He will further be compelled to believe that 

 many structures beautifully adapted to all the other parts 

 of the same creature and to the surrounding conditions, 

 have been suddenly produced; and of such complex and 

 wonderful co-adaptations, he will not be able to assign a 

 shadow of an explanation. He will be forced to admit 

 that these great and sudden transformations have left no 

 trace of their action on the embryo. To admit all this is, 

 as it seems to me, to enter into the realms of miracle, and 

 to leave those of science. 



