HAECKEL: BIOGENETIC LAW 253 



ceived as transferred back from later ones in previous periods 

 of life, or as independently acquired" (p. 121). 



Applying these principles to Crustacea, he concluded that 

 the shrimp Peneus with its long direct development gave the 

 best and truest picture of the ancestral history of the Mala- 

 costraca, and that accordingly the nauplius and the zoaea 

 larvae represented important ancestral stages. He conceived 

 it possible so to link up the various larval forms of Crustacea 

 as to weave a picture of the primeval history of the class, 

 and he made a plucky attempt to work out the phylogeny of 

 the various groups. 



The thought that development repeats evolution was 

 already implicit in the first edition of the Origin, but the 

 credit for the first clear and detailed exposition of it belongs 

 to F. Miiller. 



In much the same form as it was propounded by Miiller 

 it was adopted by Haeckel, and made the corner-stone of 

 his evolutionary embryology. Haeckel gave it more precise 

 and more technical formulation, but added nothing essentially 

 new to the idea. 



It is convenient to use his term for it the biogenetic 

 law (Biogenetische GrundgesetrJ] to distinguish it from the 

 laws of Meckel- Serres and von Baer, with which it is so 

 often confused. 



^-^ Haeckel's statement of it may best be summarised in his 

 own words, " Ontogeny, or the development of the organic 

 individual, being the series of form-changes which each 

 individual organism traverses during the whole time of its 

 individual existence, is immediately conditioned by phylogeny, 

 or the development of the organic stock (phylon) to which 

 it belongs. 



" Ontogeny is the short and rapid recapitulation of 

 phylogeny, conditioned by the physiological functions of 

 heredity (reproduction) and adaptation (nutrition). The 

 organic individual (as a morphological individual of the 

 first to the sixth order) repeats during the rapid and short 

 course of its individual development the most important of 

 the form-changes which its ancestors traversed during the 

 long and slow course of their palaeontological evolution 

 according to the laws of heredity and adaptation. 



