ORGANIC EVOLUTION 43 



There are no more remarkable instances of in- 

 dividual evolution in the whole range of animal 

 life. The fish, the reptile, the bird, the dog, and 

 the human being — all vertebrates, in short — 

 cannot for some time after their embryonic com- 

 mencement be distinguished from each other. 



* The feet of lizards and mammals, the wings and 

 feet of birds, and the hands and feet of men,' sa3^s 

 the illustrious Von Baer, as quoted by Darwdn, 



* all arise from the same fundamental form ' (8). 



* It is quite in the later stages of development,' 

 says Huxley, ' that the human being presents 

 marked differences from the ape, while the latter 

 departs as much from the dog in its development 

 as the man does ' (6). 



Not only frogs, but reptiles, birds, and mammals, 

 including man, all have gills at a certain stage 

 in their embryonic development. Nearly all the 

 lower invertebrate animals are hermaphroditic — 

 that is, in the body of each animal is found the 

 two kinds of sex organs which in the higher 

 animals exist in distinct animals. And frogs, 

 birds, and other higher animals, which as adults 

 are unisexual, have, as an inheritance from these 

 primitive forms, hermaphroditic embryos (10). 



Fourth, the fact that the structural stages through 

 which animals in embryo pass correspond in a 

 wonderful manner with the permanent structures 

 of those lower forms which extend serially back to 

 the beginnings of life. It is the proudest boast ot 

 the embryologist that he is able to know the route 

 through which any species has come to be what it 



