258 BIOLOGICAL LECTURES. 



hypotheses are found to be more satisfactory. On this point 

 I have two observations to make. 



" First, I could not abandon so beautiful a theory as that of 

 precxistent germs, to accept purely mechanical explanations. 



" Secondly, it seems to me that we should try to investigate 

 more thoroughly the manner in which development goes on 

 before seeking to discover how generation takes place." 



In 1759, Caspar Friedrich Wolff, then a young man, came 

 forward with his Theory of Generation, a powerful defence of 

 epigenesis ; but his work could avail little against such an 

 authority as Albert von Haller, whose studies on the develop- 

 ment of the chick had converted him from epigenesis to pre- 

 formation. Bonnet was confirmed in his early convictions by 

 Haller's results and conclusions, and henceforth devoted him- 

 self with increased assurance and zeal to the amplification of 

 the doctrine of preformation. 



The old objection to epigenesis, often reiterated and expa- 

 tiated upon, is strongly stated in the Tableau des Considerations 

 (Art. 14, pp. 64-66) : 



"If organized bodies are not preformed, then they must be 

 formed every day, in virtue of the laws of a special mechanics. 

 Now, I beg you to tell me what mechanics will preside over 

 the formation of a brain, a heart, a lung, and so many other 



organs .■' 



"I do not yet make the difficulty strong enough: it con- 

 sists not alone in making such or such an organ, itself com- 

 posed of many different parts, form mechanically ; it consists 

 chiefly in accounting, through the laws of mechanics alone, for 

 that multitude of varied relations which bind so closely to- 

 gether all the organic parts, and in virtue of which they all 

 cooperate to the same general end ; that is, to form that unity 

 called an animal, that organic whole which lives, grows, feels, 

 moves, maintains, and propagates itself. 



" Observe that the brain implies the heart, and that the 

 heart, in its turn, implies the brain. The brain and the heart 

 imply the nerves, the arteries, and the veins. The animal 

 nourishes itself; — the organs of circulation imply also those 

 of nutrition. The animal moves ; — the organs of movement 



