THE "GENERAL MORPHOLOGY" 219 



chapter, ^^we do not wish to draw up a body of 

 laws of organic morphology, but to give hints and 

 suggestions for drawing them up. A science that 

 is yet only in its cradle, like the morphology of 

 organisms, will have many important changes 

 to undergo before it can venture to claim for its 

 general propositions the rank of absolute and 

 unexceptionable natural laws." 



However that may be, it w^as in this provisional 

 definition of laws that the famous biogenetic law 

 first took shape, and with it a spirit entered into 

 Darwinism in the narrower sense that was never 

 again detached from its master, Haeckel. 



Let us once more take a simple illustration from 

 facts. Take a green aquatic frog and a fish, say 

 a pike. 



Both of them have a solid vertebral column in 

 their frames, and therefore both must be classed 

 amongst the vertebrates. But within the limits 

 of this group they differ very considerably from 

 each other. The frog has four well-developed 

 legs, its body terminates in a tail, and it breathes 

 by means of lungs, like a bird, a dog, or a human 

 being. The fish has fins, it swims in the water 

 by means of these fins and its long rudder-like 

 tail, and it breathes the air contain,ed in the water 

 by means of gills. When we arrange the verte- 

 brates in a series, with man at their head, it is 

 perfectly clear that the frog stands higher than the 

 fish in regard to its whole structure. It is lower 

 than the lizard, the bird, or the mammal, but at 

 the same time it is a little nearer to these three than 



