224 HAECKEL 



in two ways. In the first place it shows that we 

 were quite justified in drawing our conclusions as 

 to the past from the bird's embryonic form, even if 

 the true transitional form between the lizard and 

 the bird were never discovered at all. In the 

 second place, we see in the young bird in the egg 

 the reproduction of two consecutive ancestral 

 stages : one in the fish-gills, the other in the 

 lizard-like teeth. Once the law is admitted, there 

 can be nothing strange in this. If one ancestral 

 stage, that of the fish, is reproduced in the young 

 animal belonging to a higher group, why not 

 several? — why not all of them? No doubt the 

 ancestral series of the higher forms is of enormous 

 length. What an immense number of stages there 

 must have been before the fish ! And then we 

 have still the amphibian, the lizard, and the bird 

 or mammal, up to man. 



Why should not the law run : the whole ancestral 

 series must be reproduced in the development of 

 each individual organism ? We are now in a 

 position to see the whole bearing of Haeckel's idea, 

 and at the same time to appreciate his careful 

 restrictions of it. 



First, let us see a little of the history of the 

 matter. In the first third of the nineteenth 

 century a number of pre -Darwinian ideas of 

 evolution flitted about like ghosts in natural 

 philosophy, as I have already said. The evo- 

 lutionary ideas of Goethe and Lamarck are well 

 known to-day. Another thinker of great influence 

 was Lorentz Oken, who established the custom of 



