EPIGENESIS OR EVOLUTION. 109 



statement of morphological fact ; it is not, and does not 

 pretend to be, an explanation ,of those facts. There may- 

 be, in all probability there is, we may even go so far as to 

 say with Weismann that there must be, some great com- 

 plexity of matter underlying those gross and sensible form 

 changes which are all that the best powers of our micro- 

 scopes can make evident to our senses, but that is an 

 inference which we are at present unable to verify. Tis- 

 sues, organs, structures which can be apprehended by our 

 senses, and demonstrated, are not present as such in the 

 ovum ; they are gradually and successively established in 

 the course of ontogeny, " Alias post alias natas, ordine 

 quasque suo emergentes" just as Harvey wrote of them in 

 the seventeenth century. 



Those who now contend for an evolutionary theory 

 of development, as the only possible mode of explaining 

 the facts of heredity, occupy the same position towards 

 the doctrine of epigenesis as Wolff occupied with respect 

 to Bonnet. The argument in both cases is the same : 

 you cannot see these miniature structures, says Bonnet, 

 what right have you to say, therefore, that they do not 

 exist ? The answer of Wolff is clear and philosophical : 

 " Omnino, quidquid sensibus non patet, quod ideo non 

 existat, absolute non potest affirmari. Interim vero plus 

 elegantiar quam veritatis hoc principium habet, ad hsec 

 experimenta applicatum. Partes constitutive, ex quibus 

 omnes corporis animalis partes in primis initiis componun- 

 tur sunt globuli, mediocri microscopio cedentes semper. 

 Ouis autem diceret, se non potuisse corpus videre propter 

 exiguitatem, cujus tamen particular constituentes propter 

 exiguitatem ipsum fugere nescirent ? Nemo unquam 

 efficacioris lentis ope partes detexit quas non statim 

 vilioris notae microscopio deprehenderit. Aut enim nullo 

 modo deprehenduntur, aut satis magnae apparent. Ab- 

 sconditse igitur partes propter infinitam parvitatem, indeque 

 emergentes, fabulas sunt . . . et tandem quando incipiant 

 vasa existere, et quomodo incipiant ad oculum demonstrabo." 1 



1 C. F. Wolff, Theoria Generationis, ed. Nov. Aucta et emendata, 

 1777, P- 94- 



