I. Haeckel and His Opponents

His made his appearance in the year 1868 with his Researches as to the First Beginnings of the Vertebrate Body. His attack was primarily directed against the doctrine that the form-development of a higher organism from the first germ to the fully-developed condition can be explained from the evolution of the type. We ought not, according to him, to explain this development by regarding it as the outcome of the generations from which the single organism descends through inheritance and adaptation, but we should seek in the individual organism itself the mechanical causes of its becoming, without regard to comparative anatomy and ancestral history. His starts from the view that the germ, conceived as a uniform surface, grows unequally at different spots, and he asserts that in consequence of this unequal growth the complex structure of the organism results in the course of development. He says: “Take a simple layer and imagine that it possesses at different places a different impulse to enlargement. One will then be able to develop from purely mathematical and mechanical laws the condition in which the formation must find itself after a certain time. Its successive forms will accurately correspond to the stages of development which the individual organism runs through from the germ to the perfected condition. Thus we do not need to go beyond the consideration of the individual organism in order to understand its development, but can deduce this from the mechanical law of growth.