290 EMBRYOLOGY 



ful influence on the study of generation in plants. The question 

 which next pressed itself upon the embryologist was: Why must 

 the egg, that the young being may develop from it, first experience 

 the effect of the semen? Why must it, except in the rare cases of 

 virgin generation, be fertilized? This matter still remained a pro- 

 blem which actively demanded a solution. Ordinarily the process 

 was explained by saying that the egg, in order to begin development 

 and to divide, needed an external stimulus, and that this stimulus 

 to development was a chemical process arising either from the 

 seminal fluid or from the spermatozoa. 



Some investigators who endeavored to observe fertilization in 

 suitable objects, believed that they were able to see under the micro- 

 scope that some of the numerous spermatozoa which surrounded the 

 ovum forced their way in, dissolved, and mixing with the yolk, acted 

 as the fertilizing agent. For a time the question as to the penetra- 

 tion of the spermatozoa in the egg was the burning question of the 

 day in science. What value was laid upon the observation of a 

 spermatozoon inside the yolk-sac, may readily be seen from the fact 

 that Barry, as well as Nelson, Keber, and Meissner, called together 

 a congress of professors and doctors in order to show them the dis- 

 covery, and to permit them to see the proof for themselves. 



The state of the knowledge of generation up to the year 1875, 

 Wundt has expressed as follows in his text-book of physiology: 

 "The important condition for fertilization is, in all probability, the 

 penetration of the spermatozoa into the egg contents, which may 

 be shown in the various classes of vertebrates. After the sper- 

 matozoa have penetrated into the egg they rapidly lose their mobility 

 and dissolve themselves in the yolk. We do not possess a theory, 

 or even a plausible hypothesis, concerning the nature of the process, 

 by which after their penetration into the yolk they provoke in this 

 the process of development." 



With the year 1875, a new stage begins in the study of generation. 

 At that time I was fortunate enough during a long sojourn for study 

 at the Bay of Villafranca to determine more accurately the process of 

 fertilization, in an extraordinarily favorable object, the egg of the 

 ordinary sea-urchin, Toxopneustes lividus. 1 As in the sea-urchin the 



1 My investigations on the first stages of development in the egg of the sea- 

 urchin began Easter, 1875, in Ajaccio, where I studied especially the changes in 

 the division of the egg. At that time, however, I did not succeed in observing 

 the process of fertilization, although my attention was directed toward it. I first 

 succeeded when I went from Corsica to Villafranca, with my brother (who was 

 making a study of Radiolaria) and there continued my investigations for some 

 time. When, therefore, Bolsche, in the first volume of his encyclopaedia Men of 

 Our Time, p. 228, writes: "Oscar Hertwig made in Ajaccio the discovery of the 

 act of fertilization in the sea-urchin which will form for a long time a turning-point 

 in the history of our knowledge of the sexual act of generation, thus of one of the 

 deepest mysteries of all nature," the name of the place Ajaccio should be replaced 

 by Villafranca. 



