EIGHTH LECTURE. 



-00>S):^00 



ON CARYOKINESIS. 



By S. WATASE. 



It has been said that one of the greatest discoveries 

 of modern times is the generahzation that all animals, 

 however complex their structure, arise by the division 

 and subdivision of a single, nucleated cell. The Cell 

 doctrine in its original form, which had its origin in the 

 comparative study of adult tissues, appears in a new 

 light when viewed from the standpoint of the embryo- 

 logical history of these tissues, arising as they do, as the 

 direct products of egg-cleavage, each segment being 

 the exact copy of the original egg-cell, in so far as its 

 general, superficial features are concerned. 



Here arise two important problems : — 



(i) How does one egg, which is a single nucleated cell, 

 and which gives rise to one animal, differ from another 

 which gives rise to an entirely different organism .'* 



(2) What is the essential method of cleavage by which 

 an apparently homogeneous ovum becomes converted 

 into a complicated organism } 



The first problem is well-nigh beyond the range of 

 our present means of research. Take an egg of a star- 

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