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."[1] From the feature of unfolding this was called in the eighteenth century the theory of evolution, giving to that term quite a different meaning 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 Swammerdam's 'Biblia Naturæ,' 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 Malpighi'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, contemporaries of Swammerdam, who published in the seventeenth century the basis for this theory.
Malpighi supposed (1672) the rudiment of the embryo to preexist within the hen's egg, because he observed evidences of organization 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 considerable 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 preexist in the egg and have reached a higher development in no other way than in the eggs of plants." ("Quare pulli stamina in ovo præexistere, altiorémque originem nacta esse fateri convenit, haud dispari ritu, ac in Plantarum ovis")
- ↑ O. Hertwig.
