THE GASTRAEA-THEORY, ETC. 145 



it was allowed to fall into oblivion for a full half century, in 

 the presence of a so-called " exact " natural history. Lamarck 

 had already, with perfect precision, affirmed the common 

 origin of all organic beings from either one or a very few of 

 the simplest primitive forms. But as Darwin grounded his 

 theory of natural selection on the struggle for existence, and 

 pointed out how, under this influence, organised forms under- 

 went a constant slow transformation, so he went far beyond 

 Lamarck, and taught us to recognise the true effective causes 

 of the facts taught by T^amarck — the changes brought about 

 through inheritance and adaptability. So, also, when he 

 next proceeds to explain thereby the origin of organic species 

 and to build up a history of the development of species, he 

 must needs throw, at the same time, a quite new light on the 

 history of the development of the individual and on embry- 

 ology. The intimate connection in which these two branches 

 of the history of organic development — that of the species 

 and that of the individual — stand to each other could not 

 escape Darwin's notice. But in his great book, that had for 

 its principal object the founding of the theory of selection, 

 and also in his subsequent works (particularly in his famous 

 work on the Descent of Man), he only devotes a proportionally 

 small space to embryology, and its great significance is but 

 incidentally appreciated. 



In my general history of the development of organisms (in 

 the second volume of my ' General Morphology,' 1866) I 

 have made an attempt to establish the closeness of the inti- 

 mate relation of both branches of Biogenesis, and to point out 

 its true significance. I have there represented the palseonto- 

 logical history of the development of species — Phylogenesis or 

 genealogical history — as the true causes of the mechanical 

 efficacy of the entire developmental history of the individual 

 which Ontogenesis or germ-history in general depends upon. 

 Without the former the latter could, in general, not exist. 

 The difficult part of these relations lies in this, that the con- 

 nection between the two is a mechanico-causal one. Onto- 

 genesis is a brief recapitulation of phylogenesis, mechanically 

 dependent on the functions of inheritance and adaptability.^ 



' In my thesis on Ontoofenesis in the twentieth chapter of my ' General 

 Morphology ' (vol. 2, pp. 295 — 3U0), I have expressed this biogenetic I'uuda- 

 niental law thus : " Ontogenesis, or the developinenl of tlie organic in- 

 dividual, when the series ot alteration of form which each individual organism 

 passes tiirougti during the whole term of its individual existence, is miine- 

 diately conditional on Phylogenesis, or the development of the organic stem 

 (Pliylon) to which it itself belongs. Ontogenesis is the short and rapid 

 recapitulation of Phylogenesis dependent on the 'physiological functions of 

 inheritance (reproduction) and adaptability (nutritio?i). The organic indi- 



