io8 POPULAR SCIENCE MONTHLY. 



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 Leeuwen- 

 hoek about 1677,* of the fertilizing filaments of eggs. Soon after, con- 

 troversies began to arise as to whether the embryo preexisted in the 

 sperm or in the egg. By Leeuwenhoek, Hartsoeker ana others the 

 egg was looked upon as simply a nidus within which the sperm de- 

 veloped, 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 role. 



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 under- 

 takes 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 emboitement 

 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) con- 

 ceived 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. 



