324 The Study of Animal Life part vf 



mon to appeal to '■'■vires fortnativa^'' " hereditary tendencies," 

 and " principles of heredity," by aid of which the germ 

 grew into the likeness of the parent, and this tendency 

 to resort to verbal explanations is hardly to be driven from 

 the scientific mind except by intellectual asceticism. For 

 my own part, I prefer such " metaphysical " mist to the 

 frost of a "materiahsm" which blasts the buds of wonder. 



{c) '■'■Mystical Theories.'''' — During the eighteenth cen- 

 tury and even within the limits of the enlightened nineteenth, 

 a quaint idea of development prevailed, according to which 

 the germ (either the ovum or the sperm) contained a miniature 

 organism, preformed in all transparency, which only required 

 to be unfolded (or " evolved," as they said), in order to 

 become the future animal. Moreover, the &g% of a fowl 

 contained not only a micro-organism or miniature model of 

 the chick, but likewise in increasing minuteness similar 

 models of future generations. Microcosm lay within micro- 

 cosm, germ within germ, like the leaves within a bud 

 awaiting successive unfolding, or like an infinite juggler's 

 box to the " evolution " of which there was no end. This 

 " preformation theory" or "mystical hypothesis" was virtu- 

 ally but not actually shattered by Wolff's demonstration of 

 " Epigenesis " or gradual development from an apparently 

 simple rudiment. But the preformationists were right in 

 insisting that the future organism lay (potentially) within 

 the germ, and right also in supposing that the germ involved 

 not only the organism into which it grew but its descendants 

 as well. The form of their theory, however, was crude and 

 false. 



id) Theories of Pangenesis. — Scientific theories of here- 

 dity really begin with that of Herbert Spencer, who in 

 1864 suggested that "physiological units" derived from 

 and capable of growth into cells were accumulated from the 

 body into the reproductive elements, there to develop the 

 characters of structures like those whence they arose. At 

 dates so widely separate as are suggested by the names of 

 Democritus and Hippocrates, Paracelsus and Buffon, the 

 same idea was expressed — that the germs consist of samples 

 from the various parts of the body. But the theories of 



