Ill] THE DOCTRINE OF PREFORMATION 83 



had not essentially existed before*. In short the celebrated doctrine 

 of "preformation" implied on the one hand a clear recognition of 

 what growth can do throughout the several stages of development, 

 by hastening the increase in size of one part, hindering that of 

 another, changing their relative magnitudes and positions, and so 

 altering their forms; while on the other hand it betrayed a failure 

 (inevitable in those days) to recognise the essential difference 

 between these movements of masses and the molecular processes 

 which precede and accompany them, and which are characteristic 

 of another order of magnitude. 



The general connection, between growth and form has been 

 recognised by other writers besides Haller. Such a connection is 

 imphcit in the "proportional diagrams" by which Diirer and his 

 brother-artists illustrated the changes in form, or of relative 

 dimensions, which mark the child's growth to boyhood and to 

 manhood. The same connection was recognised by the early 

 embryologists, and appears, as a survival of the doctrine of pre- 

 formation, in Pander's I study of the development of the chick. 

 And long afterwards, the embryological aspect of the case was 

 emphasised by His J, who pointed out that the foldings of the 

 blastoderm, by which the neural and amniotic folds are brought 

 into being, were the resultant of unequal rates of growth in what 

 to begin with was a uniform layer of embryonic tissue. If a sheet 

 of paper be made to expand here and contract there, as by moisture 

 or evaporation, the plane surface becomes dimpled, or folded, or 

 buckled, by the said expansions and contractions; and the dis- 

 tortions to which the surface of the "germinal disc" is subject are, 

 as His shewed once and for all, precisely analogous. There are 



* Cf. (e.g.) Elem. Physiologiae, ed. 1766, vm, p. 114, "Ducimur autem ad 

 evolutionem potissimum, quando a perfecto animale retrorsum progredimuis et 

 incrementonim atque mutationum seriem relegimus. Ita inveniemus perfectum 

 illud animal fuisse imperfectius, alterius figurae et fabricae, et denique rude et 

 informe : et tamen idem semper animal sub iis diversis phasibus fuisse, quae absque 

 ullo saltu perpetuos parvosque per gradus cohaereant." 



t Beitrdge zur Entwickelungsgeschichte des Huhnchens im Ei, 1817, p. 40. Roux 

 ascribes the same views also to Von Baer and to R. H. Lotze {Allgem. Physiologie, 

 1851, p. 353). 



I W. His, Unsere Korperform, und das physiologische Problem ihrer Entstehung, 

 1874. See also Archiv f. Anatomie, 1894; and cf. C. B. Davenport, Processes con- 

 cerned in Ontogeny, Bull. Mus. Comp. Anat, xxvn, 1895; also G. Dehnel and 

 Jan Tur, De Embryonum evolutionis progress u ineqvuli: Kosmos (Lwow), lhi, 1928. 



