ABSTRACT
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 egg, 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 development — 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 interested 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 happened with pregnant problems in the history of science, this, too, was dealt with simultaneously by several observers, each of whom contributed his 363portion towards its solution. In the following we shall deal with Pander, who investigated the germ layers in the embryo of the hen; Rathke, who discovered the branchial slits in the embryo and the circulation in conjunction therewith; and, in another connexion, Purkinje, who discovered the germcell in the hen's egg. The first place among the creators of modern embryology, however, is held by von Baer, one of the great personalities in the field of research in the nineteenth century.
