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was ever stated in the form to which we are accustomed seems 

 to indicate the strange, one-sided view of the process of evolu- 

 tion which has passed into common thought. We have come 

 almost to think of phylogeny as a thing to be contrasted with 

 ontogeny. We are in danger of forgetting that the process of 

 phylogenetic development, as considered apart from the onto- 

 genetic, is a pure abstraction, existing nowhere except in our 

 own minds. What we have to deal with in evolution is not 

 two separate processes — an ontogenetic and a phylogenetic — 

 but simply a succession of ontogenetic processes usually each 

 exactly like its immediate predecessor, but sometimes under- 

 going a permanent modification. From each of these successive 

 processes we have mentally selected the final stage ; we have 

 arranged these stages in the order of the ontogenetic processes 

 from which they were taken, and have raised them to the dignity 

 of a separate biological process — the process of phylogenetic 

 development. Let us suppose for a moment this abstraction 

 never made, and let us regard the course of evolution in the 

 simple way as a succession of ontogenetic developments into 

 which variations of procedure have been introduced from time 

 to time. From this point we gain at once a clearer view of 

 the facts which really underlie the Biogenetic Law. If that law 

 were rigidly true in the sense that ontogenetic developments 

 were always an exact reproduction of phylogenetic history, 

 then the meaning of the law, in terms of our present method of 

 regarding evolution as a succession of modifications of onto- 

 genetic development, would be simply this : that no modification 

 had ever been introduced into ontogenetic development except 

 the addition of a further development subsequent to the com- 

 pletion of the process hitherto normal. We might, in fact, state 

 the Biogenetic Law more simply in these terms : In the course 

 of evolution ontogeny is modified only by the addition of new 

 processes at the end of development. It needs no showing that 

 such a method of procedure would inevitably result in a con- 

 dition of things rigidly consonant with the strict interpretation 

 of the law stated in the usual manner. Every stage of phylo- 

 genetic development, or, in other words, the final stage of 

 every successive ontogenetic development, would be naturally 

 embalmed in subsequent ontogenetic procedure. We recognise 

 at once that the law, as we have stated it above, is not true. 

 Ontogenetic development is sometimes modified by a change 



