Page:Encyclopædia Britannica, Ninth Edition, v. 8.djvu/175

Rh EMBRYOLOGY 165 It was reserved for Caspar Frederick Wolff (1733-1794), a German by birth, but naturalized afterwards in Russia, to bring forward observations which, though almost entirely neglected for a long time after their publication, and in some measure discredited under the influence of Haller s authority, were sixty years later acknowledged to have established the theory of epigenesis upon the secure basis of ascertained facts, and to have laid the first foundation of the morphological science of embryology. Wolffs work, entitled Theoria Generationis, first published as an inaugural Dissertation at Berlin in 1759, was republished with additions in German at Berlin in 1764, and again in Latin at Halb in 1774. Wolff also wrote a &quot;Memoir on the Development of the Intestine&quot; in Nov. Comment. Acacl Fetropol., 1768 and 1769. But it was not till the latter work was translated into German by J. F. Meckel, and appeared in his Archiv for 1812, that Wolffs peculiar merits as the founder of modern embryology came to be known or fully appreciated. The special novelty of Wolffs discoveries consisted mainly in this, that he showed that the germinal part of the bird s egg forms a layer of united granules or organized particles (cells of the modern histologist), presenting at first no semblance of the form or structure of the future embryo, but gradually converted by various morphological changes in the formative material, which are all capable of being traced by observation, into the several rudimentary organs and systems of the embyro. The earlier form of the embryo he delineated with accuracy; the actual mode of formation he traced in more than one organ, as for example in the alimentary canal, and he was the discoverer of several new and important embryological facts, as in the instance of the primordial kidneys, which have thus been named the Wolffian bodies. Wolff further showed that the growing parts of plants owe their origin to organized particles or cells, so that he was led to the great general ization that the processes of embryonic formation and of adult growth and nutrition are all of a like nature in both plants and animals. No advance, however, was made upon the basis of Wolffs discoveries till the year 1817, when the lesearches of Pander on the development of the chick gave a fuller and more exact view of the phenomena less clearly indicated by Wolff, and laid down with greater precision a plan of the formation of parts in the embryo of birds, which may be regarded as the foundation of the views of all subsequent embryologists. But although the minuter investigation of the nature and true theory of the process of embryonic development was thus held in abeyance for more than half a century, the interval was not unproductive of observations having an important bearing on the knowledge of the anatomy of the foetus and the function of reproduction. The great work of William Hunter on the human gravid uterus, containing unequalled pictorial illustrations of its subject from the pencil of Rymsdyk and other artists, was published in 1775, 1 and during a large part of the same period numerous communications to the Mtmoirs of the Royal Society testified to the activity and genius of his brother, John Hunter, in the investigation of various parts of comparative embryology. But it is mainly in his rich museum, and in the manu scripts and drawings which he left, and which have been in part described and published in the catalogue of his wonderful collection, that we obtain any adequate idea of the unexampled industry and wide scope of research of that great anatomist and physiologist. As belonging to a somewhat later period, but still before the time when the more strict investigation of embryologi- 1 Along with the work of W. Hunter must be mentioned a large collection of unpublished observations by Dr James Douglas, which are preserved in the Hiuiterian Museum of Glasgow University. cal phenomena was resumed by Pander, there fall to be noticed, as indicative of the rapid progress that was making, the experiments of Spallanzani, 1789; the researches of Autenrieth, 1797, and of Soemmering, 1799, on the human foetus; the observations of Senff on the formation of the skeleton, 1801; those of Oken and Kieser on the intestine and other organs, 1806 ; Oken s remarkable work on the bones of the head, 1807 (with the views promulgated in which Goethe s name is also intimately connected) ; J. F. Meckel s numerous and valuable contributions to embryo logy and comparative anatomy, extending over a long series of years ; and Tiedemaun s classical work on the develop ment of the brain, 1816. Christian Pander s observations were made at the instance and under the immediate supervision of Prof. Dollinger at Wiirzburg, and we learn from Von Baer s autobiography that he, being an early friend of Pander s, and knowing his qualifications for the task, had pointed him out to Dollinger as well fitted to carry out the investigation of development which that professor was desirous of having accomplished. Pander s inaugural dissertation was entitled Historia meta- morphoseos quam ovum inciibatitm prioribus quinque diebus subit, Virceburgi, 1817; and it was also published in Ger man under the title of Beilrdge zur Entu ickelungsgeschichle dts Hiihnchens im ie, Wiirzburg, 1817. The beautiful plates illustrating the latter work were executed by the elder D Alton, well known for his skill in scientific ob servation, delineation, and engraving. Pander observed the blastoderm or germinal membrane of the fowl s egg to acquire three layers of organized sub stance in the earlier period of incubation. These he named respectively the serous or outer, the vascular or middle, and the mucous or inner layers; and he traced with great skill and care the origin of the principal rudimentary organs and systems from different ones of these layers, pointing out shortly, but much more distinctly than Wolff had done, the actual nature of the changes occurring in the process of development. Carl Ernest von Baer, the greatest of modern embryolo gists, was, as already remarked, the early friend of Pander, and, at the time when the latter was engaged in his researches at Wiirzburg, was associated with Dollinger as prosector, and engaged with him in the study of comparative anatomy. He witnessed, therefore, though he did not actually take part in, Pander s researches; and the latter having after wards abandoned the inquiry, Von Baer- took it up for himself in the year 1819, when he had obtained an appoint ment in the university of Kdnigsberg, where he was the colleague of Burdach and Rathke, both of whom were able coadjutors in the investigation of the subject of his choice. (See V. Baer s interesting autobiography, published on his retirement from St Petersburg to Dorpat in 1864.) 2 Von Baer s observations were carried on at various times from 1819 to 1826 and 1827, when be published the first results in a description of the development of the chick in the first edition of Burdach s Physiology. It was at this time that Von Baer made the important dis covery of the ovarian ovum of mammals and of man, totally unknown before his time, and was thus able to prove as matter of exact observation what had only been surmised previously, viz., the entire similarity in the mode of origin of these animals with others lower in the scale. (Ejnstola de Ovi Mammalitim ft Hominu Genesi, Lipsiae, 1827. See and was educated at Dorpat and in Germany. After having been fifteen years professor in the Prussian university of Konigsberg, he was called to St Petersburg, where he remained for nesrly thirty years, and, as professor and member of the Imperial Academy, promoted m the most zealous and able manner, by his unexampled acthity, compre hensive and original views, sound judgment, and powerful co-operation, the whole range of scientific education and biological research.
 * Von Baer was born in the Russian province of Esthonia in 1792,