SECT. 3] AND EIGHTEENTH CENTURIES 201 



it doubtless arose from the fact that, in epigenesis, a continual pro- 

 duction of new organs and new relationships between organs already 

 formed would seem to require an immanent formative force of some 

 kind, such as the vis essentialis of Wolff; while, on the preformation 

 hypothesis, where embryogeny was little more than a swelling up 

 of parts already there, it could be explained as simply as nutrition. 

 The failure of the "short-cut" mechanical philosophers such as 

 Gassendi and Descartes thus led to preformationism just as much as 

 to epigenesis. A remark of Cheyne's throws much light on this 

 question, for in 17 15 he wrote, unconsciously following Gassendi's 

 line of thought, "If animals and vegetables cannot be produced 

 from matter and motion (and I have clearly proved that they can- 

 not), they must of necessity have existed from all eternity". Pre- 

 formationism was thus the only resource if the universal jurisdiction 

 of the mechanical theory of the world was to be retained. Stahl and, 

 later, Wolff, saw no point in retaining it, and carefully joined 

 together what Descartes had, with equal care, put asunder. 



The original discoveries of de Graaf and Stensen were extended 

 by Tauvry in 1690 to the tortoise, and by Lorenzini in 1678 to the 

 Torpedo', so that the eighteenth century began with an excellent 

 basis for ovistic preformationism. The greatest names associated with 

 this school were Swammerdam, Malpighi, Bonnet, v. Haller, Winslow, 

 Vallisneri, Ruysch and Spallanzani. But there were many others, 

 some of whom did valuable work, such as Bianchi, Sterre, Teichmeyer, 

 Weygand, Perrault, Vercelloni, Vidussi, Bussiere, Fizes and Cosch- 

 witz. The treatises of Imbert and Plonquet were written from this 

 point of view, as was the bright little dialogue of de Houpeville. 

 J. B. du Hamel asserted that he could see the chick embryo in the 

 Ggg before fertilisation, and Jacobaeus made a like affirmation in the 

 case of the frog. 



On the other side, that of animalculistic preformationism, the 

 contestants were fewer. Their greatest names were Leeuwenhoek, 

 Hartsoeker, Leibnitz and the cardinal de Pohgnac. In England 

 the physicians Keil and Cheque supported this position, in France 

 Geofroi and the obstetrician la Motte, in Germany Withof and 

 Ludwig, and in Belgium Lieutaud. De Superville wrote in favour 

 of it in the Philosophical Transactions of the Royal Society, and an anony- 

 mous Swedish work of some fame supported it. To the argument 

 of Vallisneri that the existence of so many animalcules must be an 



