208 BIOLOGY AND ITS MAKERS 



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,* of the fertilizing filaments of 

 eggs. Soon after, controversies began to arise as to whether 

 the embryo pre-existed 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 ovulists, who contended for the ovum in that 

 role. 



It is interesting to follow the metaphysical speculations 

 \vhich led to another aspect of the doctrine of pre-formation. 

 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 pre-formed, one 

 generation after another must be encased within it. This 

 gave rise to the fanciful idea of encasement or emboilcment, 

 which was so greatly elaborated by Bonnet and, by Leibnitz, 

 applied to the development of the soul. Even Swammerdam 

 (who, by the way, though a masterly observer, was always 

 a poor generalizer) conceived of the germs of all forthcoming 

 generations as 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 con- 



* The discovery is also attributed to Harnm, a medical student, and to 

 Hartsoeker, who claimed priority in the discovery. 



