Swammerdam (1637-1680) supplied a somewhat better basis. He observed that the parts of the butterfly, and other insects as well, are discernible in the chrysalis stage. Also, on observing caterpillars just before going into the pupa condition, he saw in outline the organs of the future stage, and very naturally concluded that development consists of an expansion of already formed parts.
A new feature was introduced through the discovery, by Leeuwenhoek about 1677,[1] of the fertilizing filaments of eggs. Soon after, controversies began to arise as to whether the embryo preexisted in the sperm or in the egg. By Leeuwenhoek, Hartsoeker and others the egg was looked upon as simply a nidus within which the sperm developed, and they asserted that the future animal existed in miniature in the sperm. These controversies gave rise to the schools of the Animalculists, who believed the sperm to be the animal germ, and of the Ovists, who contended for the ovum in that rôle.
One of the curiosities of this period is shown in Fig. 5, taken from an old Dutch edition of Leeuwenhoek's works, in which he undertakes to represent predelineation of both sexes within the sperm.
Fig. 5. Sketches illustrating Pre-delineation of the Embryo within the Sperm. From an old edition of Leeuwenhoek's Works.
It is interesting to follow the metaphysical speculations which led to another aspect of the doctrine of preformation. There were those, notably Swammerdam, Leibnitz and Bonnet, who did not hesitate to follow the idea to the logical consequence, that, if the animal germ exists preformed, one generation after another must be encased within it. This gave rise to the fanciful idea of encasement or emboîtement which was so greatly elaborated by Bonnet and, by Leibnitz, applied to the development of the soul. Even Swammerdam (who, by the way, although a masterly observer, was always a poor generalizer) conceived the mental picture of the germs of all forthcoming generations having been located in the common mother Eve, all closely encased one within the other, like the boxes of a Japanese juggler. The end of the human race was conceived of by him as a necessity, when the last germ of this wonderful series had been unfolded.
His successors, in efforts to compute the number of homunculi,
- ↑ The discovery is also attributed to Hamm, a medical student, and to Hartsoeker, who claimed priority in the discovery.
