THEORY OF NATURAL SELECTION 261 



the wings of birds or bats, or the sudden conversion of a 

 Hipparion into a horse, hardly any Hght is thrown by the be- 

 lief in abrupt modifications on the deficiency of connecting 

 links in our geological formations. But against the belief in 

 such abrupt changes, embryology enters a strong protest. It 

 is notorious that the wings of birds and bats, and the legs of 

 horses or other quadrupeds, arc undistinguishable at an early 

 embryonic period, and that they become differentiated by in- 

 sensibly fine steps. Embryological resemblances of all kinds 

 can be accounted for, as we shall hereafter see, by the pro- 

 genitors of our existing species having varied after early 

 youth, and having transmitted their newly acquired char- 

 acters to their offspring, at a corresponding age. The em- 

 bryo is thus left almost unaffected, 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 embryological resem- 

 blances, and indeed on any view, it is incredible that an ani- 

 mal 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 modi- 

 fication ; every detail in its structure being developed by in- 

 sensibly fine steps. 



He who believes that some ancient form was transformed 

 suddenly through an internal force or tendency into, for in- 

 stance, one furnished with wings, will be almost compelled 

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

 varied simultaneously. 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 pro- 

 duced ; 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 trans- 

 formations 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. 



