EPOCHS IN BIOLOGICAL HISTORY 401 



5. Embryology 



The enunciation of the cell theory came, as we have seen, 

 from combined studies on the adult structure and on the 

 development of plants and animals from the germ or egg, and 

 accordingly implies that the science of embryology has a 

 history of its own. As a matter of fact, Aristotle discussed 

 the wonder of the beating heart in the hen's egg after three 

 days' incubation, but there the subject rested until FABRICIUS 

 ( 1537-1 6 19) at Padua, early in the seventeenth century, pub- 

 lished a treatise which illustrated the obvious sequence of 

 events within the hen's egg to the time of hatching. This be- 

 ginning was built upon by a pupil of Fabricius, the cele- 

 brated Harvey, who added many details of interest, though 

 little progress in embryology was possible without the micro- 

 scope. This was first turned on the problem by the versatile 

 Malpighi in two treatises published in 1672, and at one step 

 animal development was placed upon a plane so advanced 

 that for over a century it was unappreciated. One conclusion 

 of Malpighi, however, was seized upon by contemporary 

 biologists. Apparently, unbeknown to him, some of the eggs 

 which be studied were slightly incubated, so that he thought 

 traces of the future organism are preformed in the egg. This 

 error contributed to the formulation of the preformation 

 theory, which gradually became the dominant question in 

 embryology. 



As a matter of fact the time was not ripe for theories of 

 development. The preformationists were wrong, but so were 

 Aristotle, Harvey, and others who went to the opposite ex- 

 treme and denied all egg organization and therefore tried to 

 get something out of nothing. It remained, as we know, for 

 the present generation of embryologists to work out many of 

 the details of the origin and organization of the germ cells, 



