to imply that embryologists therefore are an order of scientists superior to all others. Embryology is so vast and varied that it offers problems adapted, I might almost say, to every size of mind, and persons of moderate capacity, as well as those of the highest gifts of genius, can find adequate opportunity to gratify successfully in the field of embryology any demon of research which may possess them.
Let us first consider some of the conditions upon which the progress of embryological science has depended. Of course the first and all-essential thing is the amount and quality of human ability which has gone into it. This is true of every science, as goes without saying. It may, however, be interesting to pause a moment, since contemporary events are directing so much of the interest of the world towards Russia, in order to point out that modern scientific embryology had its birth in that country, for the first step was the publication of the articles by C. F. Wolff on the 'Theory of Generation and the Development of the Intestine in the Chick'; and the second and more important step was the publication of the great work of Carl Ernst von Baer, which may be said without exaggeration to have created by itself a new science. Von Baer's treatise on the 'Entwicke-lungsgeschichte der Thiere' is one of the greatest works in the whole history of biological science, and established the author's reputation as a genius of research. By the aid of improved methods a tyro in embryology may now verify von Baer's discoveries, but there has been no one since von Baer, who could have approached with his scientific resources the magnitude of his achievement. Let us then honor his memory. Although Wolff and von Baer, both, were Russian subjects, they were of German descent, and we find indeed that throughout the greater part of the last century the advance of embryology was due chiefly to German investigations.
How recent this knowledge is we are apt to forget. From 1800 to 1840 the seminal animalcules were universally regarded as parasites. The fact that they are normal products of the testis and the true male sexual elements was first discovered in 1841 by the Swiss anatomist von Kölliker, who was a leader in microscopical research for sixty-five years, and whose death occurred last year. Of Kölliker it may be asserted safely that he knew more by direct personal observation of the microscopical structure of animals than any one else who has ever lived. He was much honored in Europe. The last time I met him was at the International Zoological Congress at Berne, in 1894. It was most impressive to see all the members of the congress spontaneously rise to their feet when the handsome old man unexpectedly entered the meeting. The fact that the spermatozoon enters the ovum and produces the so-called male pronucleus, the union of which with the female pronucleus completes the act of fertilization, was finally demonstrated only in 1875 by Oscar Hertwig. These two