MODERN BIOLOGY 517 



the larva: now succeed one another, whereas the history of the river crayfish 

 has been obliterated and that of a number of other Crustacea has received 

 fresh contributions in respect of form. 



This theory, which Fritz Miiller expounded in 1S64 in a paper entitled 

 Fur Darwin, aroused Haeckel's ardent enthusiasm. To him it became a "prin- 

 ciple for the origin of life," the main support of the theory of descent and 

 a particularly weighty argument in the controversy over the struggle for 

 man's "natural creation." It was then chiefly to human evolution that he 

 sought to apply the theory and in his Anthrofo genie, as also previously in 

 his Naturliche Schopfungs geschichte , he works out the embryonic development 

 of man from the es,g to birth with a view to collecting proofs of the condi- 

 tions governing man's descent and affinity. Haeckel was never a specialist 

 in embryology and its points of detail were of no interest to him in them- 

 selves, but only in so far as they could serve as evidence to prove the descent 

 of man. His ideas of embryology could in such circumstances only be one- 

 sided and deficient; the professional embryologists offered serious objections 

 to them, which he either affected to overlook or else answered with per- 

 sonal abuse. Complaints were made especially against his illustrations, 

 which, contrary to usual practice, he hardly ever borrowed from mono- 

 graphs on the subject, but drew himself. Being designed exclusively to prove 

 one single assertion, his illustrations were naturally extremely schematic and 

 without a trace of scientific value, sometimes indeed so far divergent from 

 the actual facts as to cause him to be accused of deliberate falsification — • 

 an accusation that a knowledge of his character would have at once refuted.' 



Haeckel's theory of germinal layers and gastrcea 

 Two specially remarkable details in Haeckel's doctrine of the biogenetical 

 principle are the theory of the germinal layers and the gastrasa theory. We 

 have previously described the investigations into the embryonic germinal 

 layers carried out by Pander, von Baer, Remak, and others, and also how 

 Huxley compared dermal and intestinal layers in the medusa: with the ger- 

 minal layers in higher animals. Besides these facts Haeckel had for material 

 on which to work his own researches into the Calcarea, the embryonal de- 

 velopment of which he had studied. On all this he now bases the theory of 

 the origin of the animals, and especially that of man; since man originates 

 from a single cell, the ^gg, then in the beginning of time the original form 

 out of which the human race has evolved must also have been a unicellular 

 animal. Out of the egg-cell there is developed by segmentation a cell-group; 



^ It is nevertheless difficult to understand such an action as this : allowing in his Naturliche 

 Schopfungsgeschichte (ed. i, p. 241) the same cliche, reproduced three times, to represent an egg of 

 a man, an ape, and a dog. This absurdity was removed from subsequent editions, albeit only 

 after Haeckel had rewarded with abuse those who pointed out the fact; and the incident was for 

 ever afterwards a theme on which his enemies constantly harped. 



