14 INTRODUCTORY I 



process is one o f metamorphosis ' or the simultaneous origin of 

 all parts. In genei'ation properly so called, however in the 

 development of the Chick, for example the process f a parte 

 aliqua, tanquam ab origine, incipit ; eiusque ope reliqua membra 

 adsciscuntur : atque liaec per epigenesin fieri dicimus : sensim 

 nempe, partem post partem ', and this ' pars prima genitalis ' 

 Harvey held, in opposition to Aristotle, to be the blood. 1 



But in spite of the exact observation and brilliant exposition 

 of his followers, the teaching of Aristotle was destined to be 

 overshadowed and eclipsed, temporarily at least, by a new hypo- 

 thesis which, appearing first towards the end of the seventeenth 

 century, swept the schools and universities, and dominated 

 biological speculation for a hundred years. 



This was the theory of Evolution or Preformation. According 

 to it the future animal or plant is already present in miniature 

 in the germ with all its parts complete, invisible or hardly visible 

 it may be, but still there, and not merely 'potential; and in 

 development there is no such thing as ' generation ', but only 

 growth, whereby that which was before impalpable and invisible 

 becomes tangible and manifest to our eyes. A further and 

 logical outcome of the hypothesis was the doctrine of 'emboite- 

 ment', enthusiastically described by Bonnet as <une des plus 

 belles victoires que Fentendement pur ait remporte sur les sens '? 

 The organism present already in the germ, with all its parts 

 complete, possesses of necessity the germs of the next generation, 

 and so on in indefinite though not in infinite regress, for as 

 Bonnet is careful to tell us, ' II ne faut pas supposer un emboite- 

 ment a Pinfini, ce qui seroit absurde. La divisibilite de la 

 matiere a Finfini par laquelle on pretendroit soutenir cet em- 

 boitement est une verite" geometrique et une erreur physique/ 3 

 Swammerdam solved the difficulty in another way. All the 

 germs of the human race must have been present in the bodies 

 of our first parents, and 'exhaustis his ovis human i generis 

 finem adesse'. 4 



The theory became widely held. First put forward by Marcello 



1 Harvey, 1. c., Ex. 50. 



2 Bonnet, Cont. de la nat., 7 me partie, c. ix ; (Euvres, vol. iv, p. 270. 

 8 Bonnet, Consid. sur les corps org., c. viii ; CEuvres, vol. iii, p. 74. 



4 Swammerdam, 1679, pp. 21, 22. 



