HISTORICAL SKETCH 3 



or longitudinal elements these fibrils were wound in the form of a close 

 spiral, while the vessels themselves were bound together by a transverse 

 series of interwoven threads. He accordingly compared the structure 

 of the plant with that of a basket, and with "fine bone-lace, when the 

 women are working it upon the cushion" (p. 121). 



Antony van Leeuwenhoek (1632-1723) of Delft is remembered for 

 his pioneer researches in the field of microscopy. He constructed a 

 number of simple lenses of high power, and with these he was able to see 

 for the first time certain protozoa, bacteria, and other minute forms of life. 

 In the course of his investigations he observed the cells ("globules") 

 in the tissues of higher organisms. His work, in spite of the fact that 

 it was carried on without any definite plan, brought to light a number 

 of important facts, but in general his accomplishments do not bear 

 favorable comparison with those of Grew and Malpighi. 



Preformation and Epigenesis. After the death of Leeuwenhoek 

 there ensued a period during which the actual investigation of the cell 

 and the structure of organisms remained practically at a standstill. At 

 that time, however, certain speculations were indulged in which should 

 be recorded here, not because they can be regarded as scientific cytology 

 but because of the influence they exerted upon the formulation of many 

 cytological problems in later years. These speculations resulted in the 

 division of the biologists of the day into two schools, the main question 

 at issue being the manner in which the embryo develops from the egg. 

 The two theories formulated in answer to this question have been called 

 the Preformation Theory and the Theory of Epigenesis. 



According to the Preformation Theory, the basis for which was laid 

 in the seventeenth century works of Swammerdam, Malpighi, and 

 Leeuwenhoek, the egg contains a fully formed miniature individual, 

 which simply unfolds and enlarges as development proceeds. Because 

 of this unfolding the theory was also known as the Theory of Evolu- 

 tion, a phrase which has a quite different connotation today. In the 

 eighteenth century the preformation idea was carried to an absurd 

 extreme by Bonnet (1720-1793) and others, who argued that if the egg 

 contains the complete new individual, the latter must in turn contain 

 the eggs and individuals of all future generations successively encased 

 within it, like an infinite series of boxes one within another. This theory 

 of encasement (emboitement) was a logical deduction from the since 

 abandoned premise that everything, including organisms for all time, 

 had been formed by one original creation, and that nothing could there- 

 fore be formed anew. The preformationists soon became separated into 

 two groups: the spermists or animalculists, and the ovists. By the 

 former the new individual was supposed to be encased in the sperma- 

 tozoon, and figures were actually published showing a small human figure, 

 or "homunculus," within the sperm head. The ovists, on the contrary, 



