196 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11 



the primitive germs which were made at the original creation and 

 that germs organised Hke animals do by no means pre-exist, for if 

 they did, molae uterinae, encysted tumours, and the like, could not 

 come into being." Haller then goes on to describe Needham's 

 experiments with meat broths, etc., and objects to his "system", 

 largely on the ground that "blind forces without any intelligence 

 could hardly be able to form animals for ends foreseen and ready 

 to take their places in the scheme of beings". He considers that 

 Needham's theories are completely disproved by experiments such 

 as those of Spallanzani, though, curiously enough, he does not quote 

 the latter author in this connection. I shall return to this later. 



"Nobody", he goes on to say, "has upheld epigenesis more than 

 M. Wolff, who has undertaken an examination to demonstrate that 

 plants and animals are formed without a mould out of matter by a 

 certain constant force which he calls 'essential' [in his Theoria 

 Generationis] .... I have indeed seen many of the phenomena which 

 he describes, and it is certain that the heart seems to be formed out 

 of a congealed humour and that the whole animal appears to have 

 the same consistency. But it does not follow that because this 

 primitive glue which is to take on the shape of the animal does not 

 appear to possess its structure and all its parts, it has not effectively 

 got them. I have often given greater solidity to this jelly by the use 

 merely of spirits of wine and by this means I saw that what had 

 appeared to me to be a homogeneous jelly was composed of fibres, 

 vessels, and viscera. Now surely nobody will say that the vis 

 essentialis of the spirit of wine gave an organic structure to an un- 

 formed matter, on the contrary it is rather in the removal of trans- 

 parency and the accession of greater firmness to the extremities, as 

 well as the making of a more obvious boundary to the contour of 

 a viscus that one could see the structure of a cellular tissue, which 

 was ready to be formed but which the transparency had previously 

 hidden and the wetness not allowed to be circumscribed by lines. . . . 

 Finally, to cut a long story short, why does this vis essentialis, 

 which is one only, form always and in the same places the parts of 

 an animal which are so different, and always upon the same model, 

 if inorganic matter is susceptible of changes and is capable of taking 

 all sorts of forms? Why should the material coming from a hen 

 always give rise to a chicken, and that from a peacock give rise to 

 a peacock? To these questions no answer is given." This was the 



