VON BAER AND RISE OF EMBRYOLOGY. 107 



parts of the flower, such as stamens and colored petals, are enveloped 

 by the green and still undeveloped sepals, — just as the parts grow in 

 concealment and then suddenly expand into a blossom, so also in the 

 development of animals it was thought that the already present small 

 but transparent parts grow, gradually expand, and become discernible."* 

 From the feature of unfolding this was called in the eighteenth cen- 

 tury the theory of evolution, giving to that term quite a different mean- 

 ing from that accepted at the present time. 



This theory, strange as it may seem to us now, was founded on a 

 basis of actual observation — not entirely on speculation. Although it 

 was a product of the seventeenth century, from several printed accounts 

 one is likely to gather the impression that it arose in the eighteenth 

 century and that Bonnet, Haller and Leibnitz were among its founders. 

 This implication is in part fostered by the circumstance that Swam- 

 merdam's ' Biblia Naturae,' which contains the germ of the theory, 

 was not published until 1737 — more than a half century after his 

 death — although the observations for it were completed before Mal- 

 pighi's first paper on embryology was published in 1672. While it 

 is well to bear in mind that date of publication, rather than date of 

 observation, is accepted as establishing the period of emergence of 

 ideas, there were other men, such as Malpighi and Leeuwenhoek, con- 

 temporaries of Swammerdam, who published in the seventeenth cen- 

 tury the basis for this theory. 



Malpighi supposed (1672) the rudiment of the embryo to pre- 

 exist within the hen's egg, because he observed evidences of organiza- 

 tion in the unincubated egg. This was in the heat of the Italian 

 summer (in July and August, as he himself records), and Dareste 

 suggests that the developmental changes had gone forward to a con- 

 siderable degree before Malpighi opened the eggs. Be this as it may, 

 the imperfection of his instruments and technique would have made it 

 very difficult to have seen anything definitely in stages under twenty- 

 four hours. 



In reference to his observations he says that, in the unincubated 

 egg, he saw a small embryo enclosed in a sac which he subjected to 

 the rays of the sun. " Frequently I opened the sac with the point 

 of a needle so that the 'animals contained within might be brought 

 to the light, nevertheless to no purpose: for the individuals were so 

 jelly-like and so very small that they were lacerated by a light stroke. 

 Therefore it is right to confess that the beginnings of the chick pre- 

 exist in the egg and have reached a higher development in no other 

 way than in the eggs of plants." (" Quare pulli stamina in ovo 

 prceexistere, altioremque originem nacta esse fateri convenit, haud dis- 

 pari ritu, ac in Plantarum ovis") 



* 0. Hertwig. 



