5 42. THE HISTORY OF BIOLOGY 



consummate form. On the other hand, a number of scientists of today, 

 some of them admittedly of the highest rank, working all at the same time 

 in mutual rivalry at the problem of fertilization, expound their results 

 practically every year, often in a half-finished state and sadly in need of 

 emendation, and then disputing each other's claim to the honour of hav- 

 ing produced the various details of the discovery, each one seeking to inter- 

 pret according to his own lights statements that are often found to have 

 been originally formulated as mere assumptions and suggestions. The account 

 of how our knowledge of the origin of individual life was finally acquired 

 can therefore hardly be so attractive a task as that of describing Harvey's 

 lifework. 



That science had so long to wait before the phenomena of fertilization 

 were fully elucidated is, of course, primarily due to the fact that the knowl- 

 edge of its basis, the cell, was for so long incomplete. And in particular the 

 idea as to the nature of the nucleus of the cell was, as O. Hertwig so weightily 

 observes, still extremely vague as late as in the seventies; a cystic, homogene- 

 ous formation was seen in the middle of the cell, and no really clear idea was 

 obtained as to its meaning. It was supposed to have been observed that on 

 certain occasions this formation disappeared and that this was particularly 

 so within the egg-cell; moreover, it was postulated by Haeckel's biogeneti- 

 cal principle, according to which every living being arises out of an entirely 

 undifferentiated mass of plasm. It was thought to be probable that sperma- 

 tozoa, one or several, penetrate the egg upon fertilization, but the part they 

 played in the process was utterly vague; on the whole, it was deemed suffi- 

 cient to assume some kind of chemical or physical influence upon the egg- 

 cell, whereby its stages of segmentation, which had already been studied, 

 were produced. Indeed, the phenomena of nuclear division, referred to above, 

 had been partially investigated in the case of egg-cells; Fol particularly had 

 observed radial phenomena accompanying division, and Biitschli the actual 

 nuclear pole, but no one had as yet gained any clear idea of the process. 



In 1875 O. Hertwig spent some months by the Mediterranean Sea and 

 there discovered an object particularly suitable for studies in fertilization 

 and egg-development in the sea-urchin, whose eggs are transparent, occur 

 in large numbers, and are rapidly developed. The results he obtained from 

 his investigations of this material he recorded in a dissertation written for 

 the purpose of obtaining a lectureship at Jena. Among the theses that ac- 

 companied the paper, according to the German custom, the first runs as 

 follows : ' ' Die Befruchtung beruht auj der Verschmelzung von geschlectlkh differen- 

 Xierten Zellkernen." This statement, upon which further light is thrown in the 

 paper itself, really contains the essence of our modern theory of fertilization. 

 There is indeed still another of these theses that is of importance: the as- 

 sertion that the egg does not pass through any ' ' monera ' ' stage — a statement 



