THE "GENERAL MORPHOLOGY" 2^7 



parallel stems diverge, that of the animals and 

 that of the plants ; they never touch each other 

 after this point, and so cannot be expected to be 

 reproduced in the embryonic forms. Then the 

 animal stem is split up almost at the root into at 

 least five independent branches, each of which 

 pursues its separate line of development. One 

 culminates in the insects, above the worms and the 

 Crustacea. A totally independent stem issues in 

 the vertebrates, and this in turn breaks into many 

 different branches. Beyond the lizards, for instance, 

 we find the development of the mammals and birds, 

 which run on as separate and parallel lines. It 

 was mere nonsense to expect a mammal in its 

 embryonic development to assume the form of 

 a bird, or a crab, or a beetle, or a mussel, or a 

 medusa, even if the biogenetic law were estab- 

 lished ten times over. 



The second mistake made by Oken was to 

 declare that, whatever it cost, the law must be 

 observed everywhere. He examined the butterfly. 

 It passed through two curious embryonic stages : 

 first the caterpillar, then the pupa. The caterpillar 

 corresponded to the worm ; that might be plausibly 

 contended. But the pupa also must stand for 

 something. Between the worm and the insect in 

 classification was the crustacean. It had a hard 

 shell : so had the pupa. Consequently, the pupa 

 is a reproduction of the crustacea-stage. Such 

 were the bold chess-moves of the older theorist. 



Haeckel first established that there was such a 

 thing as the biogenetic law. There is a funda- 



