A HISTORY OF SCIENCE 



organisms are built, so to speak that is, out of which 

 all have evolved. 



This gastrula theory, now generally accepted, is one 

 of Haeckel's two great fundamental contributions to 

 the evolution philosophy with the history of which his 

 life work is so intimately linked. The other contribu- 

 tion is the theory, even more famous and now equally 

 undisputed, that every individual organism, in its em- 

 bryological development, rehearses in slurred but un- 

 mistakable epitome the steps of evolution by which 

 the ancestors of that individual came into racial being. 

 That is to say, every mammal, for example, originating 

 in an egg stage, when it is comparable to a protozoon, 

 passes through successive stages when it is virtually in 

 succession a gastrula, a fish, and an amphibian before 

 it attains the mammalian status, because its direct an- 

 cestors were in succession, through the long geological 

 ages, protozoons, gastrulas, fishes, amphibians before 

 the true mammal was evolved. This theory cast a 

 flood of light into many dark places of the Darwinian 

 philosophy. It was propounded in 1866 in Professor 

 Haeckel's great work on morphology, and it has ever 

 since been a guiding principle in his important philo- 

 sophical studies. 



It was through this same work on morphology that 

 Haeckel first came to be universally recognized as 

 the great continental champion of Darwinism the 

 Huxley of Germany. Like Huxley, Haeckel had at 

 once made the logical application of the Darwinian 

 theory to man himself, and he sought now to trace the 

 exact lineage of the human family as no one had hither- 

 to attempted to fathom it. Utilizing his wide range 



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