222 HAECKEL 



higher in classification than the fishes, were 

 developed from the fishes in earlier ages in the 

 course of progressive evolution. Once upon a time 

 they were fishes. If that is so, the curious 

 phenomenon we have been considering really 

 means that each young frog resembles its fish- 

 ancestors. In each case to-day the frog's egg first 

 produces the earlier or ancestral stage, the fish. 

 It then develops rapidly into a frog. In other 

 words, the individual development recapitulates 

 an important chapter of the earlier history of the 

 whole race of frogs. Putting this in the form of 

 a law, it runs : each new individual must, in its 

 development, pass rapidly through the form of its 

 parents' ancestors before it assumes the parent form 

 itself. If a new individual frog is to be developed, 

 and if the ancestors of the whole frog-stem were 

 fishes, the first thing to develop from the frog's egg 

 will be a fish, and it will only later assume the form 

 of a frog. 



That is a simple and pictorial outline of what 

 we mean when we speak of "the biogenetic law." 

 We need, of course, much more than the one 

 frog-fish fact before we can erect it into a law. 

 But we have only to look round us, and we find 

 similar phenomena as common as pebbles. 



Let us bear in mind that evolution proceeded 

 from certain amphibia to the lizards, and from 

 these to the birds and mammals. That is a long 

 journey, but we have no alternative. If the 

 amphibia (such as the frog and the salamander) 

 descend from the fishes, all the higher classes up 



