A CRITICAL RE-STATEMENT OF THE BIOGENETIC LAW. 99 
V. The life-cycle is extended, not by addition of a new adult stage at the 
end of the old adult stage, but by further differentiation of organs 
or parts of organs. Old adult characters are eliminated from the 
ontogeny unless required as temporary bases for the new characters. 
Vr. -As the individual, tlirough all the form-changes of his life-cycle, is an 
evolutional and functional unity, modifications manifested in his 
larval or adult phases involve co-ordinating changes in the more 
passive and formative phases (embr3ronic, post-larval, pupal stages). 
VII. ThuS; while a given ontogeny, under normal conditions, tends to 
repeat the form-sequences of its predecessors, it is liable to changes 
in every part of the life-cycle — -positively, by equipping the larval 
and adult stages for the changing conditions of their various careers, 
or with greater efficiency for the same conditions, and negatively, 
by abTjreviating the formative processes to the uttermost. 
VIII. The idea that form-changes in ontogeny were preceded by similnr 
changes in adult ancestry is an illusion, since adult Metazoan 
ancestors never directly gave rise to their successors, but to gametes ; 
and these, blended with other gametes, were the real heralds of 
successive ontogenies. Plainly the first Metazoan was not produced 
by a Metazoan. He was the result of a Protozoan ontogen}', the 
tour lie force of a genius among Protozoan zygotes. The first Bird 
was hatched from a Reptile's egg. We can speak of earlier and 
later, original and modified, ontogenetic processes ; but the possi- 
bility of a distinction between ancestral and ontogenetic processes 
is out of the question. All changes are ontogenetic. 
IX. In the same way the contrast between " palingenetic " (repetitive of 
adult ancestry) and " cenogenetic " (foreign or nou-repetitive) 
characters, which was originally based by Haeckel on an assumed 
hereditary difference between adult changes and embryonic adap- 
tations, has lost its significance. Both types of character were of 
ontogenetic origin, and equally hereditary, but the one set arose 
earlier in the phyletic history than the other. Morphology u ill not 
recover exactitude of outlook until it is entirely freed from the 
hypnotic influence of Haeckel's terminology. I propose in future 
to use palceogenetic and neogenetic when referring to ontogenetic 
processes, and palieomorphic and neomorpliic when contrasting 
primitive and modified types of structure. 
X. There is a general correspondence between the successive grades of 
differentiation in ontogeny and the successive types of organisation 
which characterise the steps of phyletic progress (Meckel's 
law). This general correspondence exists because each series — the 
ontogenetic and the phyletic — was preceded and caused by the same 
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