176 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



zation had to be retained, there remained nothing except to 

 strengthen the ordinary process of egg-maturation and thus 

 to endow the retained half of the germ-plasm with increased 

 powers of growth. 



III. Amphimixis as the Significance of Conjugation and 

 Fertilization. 



The Facts of Conjugation. 



Biologists have been, for some time, in the habit of comparing 

 the conjugation of unicellular organisms with the sexual repro- 

 duction of multicellular forms of life, and of regarding them as 

 to some extent equivalent. There was an obvious comparison 

 between the more or less complete fusion of two of the former, 

 and the coalescence of the two sexual cells of the latter ; and this 

 conception was strengthened when observation appeared to 

 prove that the reproduction of unicellular beings by means of 

 fission could not continue indefinitely, unless conjugation took 

 place from time to time. Conjugation was looked upon as a 

 ' fertiHzing ' process which endowed the organism anew with the 

 capacity for fission, not once only but repeatedly, just as fertiliza- 

 tion in multicellular beings renders possible the production of 

 numerous cell-generations, constituting embryogeny. The cell 

 material which, in the latter case, is made use of in building up 

 the multicellular organism, appears in the former as a succession 

 of many generations of unicellular beings ; but, in both cases, 

 the capacity for such cell multipHcation depends upon the pre- 

 vious occurrence of a fusion of cells, thus originating the life- 

 giving force which renders reproduction possible. 



The above sentences form an approximate statement of the 

 views which, with some individual differences, have obtained 

 among biologists during the decade before the last. Even the 

 remarkable discoveries of Biitschli on the conjugation of Infu- 

 soria led to no essential modification, although they taught us to 

 recognize the mysterious nuclear changes, the analogy of which 

 to the processes of fertilization was then unknown. 



However, mainly in consequence of the observations of the 

 brothers Hertwig, of Fol and of E. van Beneden, this analogy is 

 now recognized, and we may admit that the connection between 



