82 PROF. W. GARSTANG ON THE THEORY OF RECAPITULATION : 
conception o£ evolution was wedded, fifty years ago, to cuiTent ideas of 
ancestry, heredity, and development : Ancestors created, heredity transmitted, 
and development repeated the order of creation. 
2. To Haeckel, phylogenesis meant " the chain of manifold animal forms 
which represent the ancestry " of an organism, i. e. the phyletic line of 
succession of adults. Ontogenesis was, and is, tlie succession of form- 
changes between zygote and adult of the same organism. The ontogenetic 
sequence was regarded as resembling, and actually caused by, the phyletic 
sequence of adults, which had preceded it. 
3. But Haeckel overlooked the other evolutionary sequence, the phyletic 
line of succession of zygotes, running more or less parallel with the adult 
sequence, step by step, though steadily diverging. Every elaboration of 
adult form, even of its degree of pliability under environmental influence 
(for there are great differences among animals, as among plants, in this 
respect), was preceded by a corresponding elaboration of zygotic structure *, 
nuclear or cytoplasmic or both, determining, under suitable conditions, the 
form and character of the ontogenetic changes and their result. Through 
the whole course of Evolution, every adult Metazoan has been the climax of 
a separate ontogeny or life-cycle, which has always intervened between adult 
and adult in that succession of forms which Haeckel terms "Phylogenesis." 
The real Phylogeny of Metazoa has never been a direct succession of adult 
forms, but a succession of ontogenies or life-cycles. 
4. This was so from the very beginning, when zygote and adult were 
indistinguishable in form as ancestral Flagellate Protozoa. Zygosis must 
have been followed, then as now, by successive cell-divisions, corresponding 
to the cell-divisions of Metazoan ontogeny, though they led to no single 
multicellular adult. A stage further on, the corresponding cell-divisions 
gave rise to adherent colonies, fixed or free, arborescent or epithelial, each 
type established by its own ontogeny. The very first, most ancestral 
Metazoan of all — at whatever grade of evolution the dividing line may be 
drawn — must be admitted to have been built up by a full ontogeny from 
unicellular zygote to multicellular adult, so that, in the first, as in the latest 
Metazoan, ontogeny came first, leaving the first adult Metazoan as its original 
achievement. The next generation, through a new ontogeny, produced a 
second adult, and so on. In a word, Haeckel's causes and effects must be 
inverted. Phylogeny (in Haeckel's sense) is the product, the " record " — 
not the precedent cause — of successive ontogenies ; and neither the first, nor 
the second, of Haeckel's phrases can any longer express the basis of true 
biogenetic law. Ontogeny does not recapitulate Phylogeny : it creates it. 
* Cf. Hertwig (1906, i. p. 5G) : " Die Eizelle z. B. eines jetzt lebendeii Saiig'etieres ist 
kein einfaches uiid iudifFerentes, bestimmungsloses Gebilde .... sondern .... das ausser- 
ordentlicli komplizierte Endprodukt eines sehr langen, liiatorisclien Entwickelungsprozesses." 
