CHAPTER V 



THE PROGRESS OF EMBRYOLOGY 



Ovists and animalculists 



THE MOST IMPORTANT FEATURES of the earlier history of embryology 

 have already been referred to in previous sections of this work — how 

 even Hippocrates had observed the development of the hen's Qgg, how 

 Aristotle studied the embryology of various animals, how Fabricius, 

 Harvey, Malpighi, and C. F. Wolff each in turn made valuable contributions 

 to the knowledge of the development of the embryo, especially in the hen's 

 egg, which had remained throughout the most easily available object of 

 investigation, but also in a number of other animals, chiefly, of course, 

 mammals. These inquiries were naturally much influenced by the speculations 

 on the process of development that succeeded one another during different 

 epochs; in this respect, the "preformation" theory, which prevailed for a 

 time, had a most unfavourable effect, seeing that its champions, for obvious 

 reasons, cared but little for practical observations of the embryonic develop- 

 ment — everything having been ready-formed from the beginning, there 

 was, of course, no need for observation. This explains why the eighteenth 

 century, during which the preformation theory held sway, proved so barren 

 in embryological observations; instead of investigating, scientists wasted 

 their time in profitless speculations and controversies between ovists and 

 animalculists. Some of the latter certainly reached the height of absurdity 

 when they saw in the spermatozoa the true agents of reproduction, with the 

 consequence that they succeeded in distinguishing under the microscope in 

 every human spermium, with the aid of their imaginations, a complete 

 miniature human being with all the limbs ready formed. It was not until 

 the close of that century that embryology received a fresh impetus; C. F. 

 Wolff made a beginning with his, certainly exaggerated, epigenesis theory 

 and his embryological observations based thereon; Cuvier, who was in- 

 terested in all biological problems, also made weighty contributions to this 

 subject; Blainville has just been mentioned as a promoter of embryological 

 research; nevertheless, science has mainly to thank certain German scientists 

 for its most important progress in this direction, progress which, in fact, 

 gave rise to an essentially new view of life-phenomena. As has often hap- 

 pened with pregnant problems in the history of science, this, too, was dealt 

 with simultaneously by several observers, each of whom contributed his 



