2IO EMBRYOLOGY IN THE SEVENTEENTH [pt. ii 



a Jesuit and who had drawn materialistic inferences from his writings, 

 contained the following passage: "The numerous absurdities which 

 exist in the opinion ofpre-existent germs together with the impossibility 

 of explaining on that ground the birth of monsters and hybrids, made 

 me embrace the ancient system of epigenesis, which is that of Aristotle, 

 Hippocrates, and all the ancient philosophers, as well as of Bacon 

 and a great number of savants among the neoteriques. My observa- 

 tions also led me directly to the same result". Needham's embryology 

 is mostly contained in his Observations nouvelles sur la Generation of 

 1750. He was explicitly a Leibnitzian and postulated a vegetative 

 force in every monad. 



Needham was not the only thoroughgoing epigenesist of this 

 period. Maupertuis, whose Venus Physique was published anony- 

 mously in 1746, came out very clearly on the side of epigenesis. 

 "I know too well", he said, "the faults of all the systems which I 

 have been describing, to adopt any one of them, and I find too 

 much obscurity in the whole matter to wish to form one of my own. 

 I have but a few vague thoughts which I propose rather as thoughts 

 to be examined than as opinions to be received, and I shall neither 

 be surprised nor think myself aggrieved if they are rejected. It seems 

 to me that both the system of eggs and that of spermatic animal- 

 cules are incompatible with the manner in which Harvey actually 

 saw the embryo to be formed. And one or the other of these systems 

 seems to me still more surely destroyed by the resemblance of the 

 child, now to the father and now to the mother, and by hybrid 

 animals which are born from two different species. ... In this ob- 

 scurity in which we find ourselves on the manner in which the foetus 

 is formed from the mixture of two liquors, we find certain facts which 

 are perhaps a better analogy than what happens in the brain. When 

 one mixes silver and spirits of nitre with mercury and water, the 

 particles of these substances come together themselves to form a 

 vegetation so like a tree that it has been impossible to refuse it the 

 name." This was the Arbor Dianae, which played a great part in 

 these embryological controversies of the eighteenth century. It has 

 a great interest for us, for it was perhaps the first occasion on which 

 a non-living phenomenon had been appealed to as an illustration 

 of what went on in the living body. It is true that Descartes long 

 before had said that the movements of the living body were carried 

 out by mechanisms like clocks or watches, and that they resembled 



