6 POPULAR SCIENCE MONTHLY 



to imply that embryologists therefore are an order of scientists superior 

 to all others. Embryology is so vast and varied that it offers prob- 

 lems 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 anato- 

 mist von Kolliker, who was a leader in microscopical research for 

 sixty-five years, and whose death occurred last year. Of Kolliker it 

 may be asserted safely that he knew more by direct personal observa- 

 tion 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 unex- 

 pectedly 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 



