rilE BIOLOGY OF THE CELL SURFACE 



Before I begin the discussion I should like again to point 

 out how necessary it is that we appreciate diflFerences 

 normally appearing in biological processes before we 

 attempt to evaluate these processes. With respect to the 

 process of cell-division, we recognize two kinds. Based 

 upon the behavior of the nucleus in cell-division as a criter- 

 ion, two categories of cell-division have been set up: that 

 with direct (amitotic) and that with indirect (mitotic) 

 division of the nucleus. 



In direct or amitotic nuclear division, the nucleus by 

 constriction separates into two parts. It first elongates, 

 taking the form of a dumb-bell or hour-glass, and then 

 breaks into two equal or unequal portions. Each of these 

 with cytoplasm constitutes a new cell, if the cytoplasm also 

 divides. But division of the cytoplasm synchronously 

 with that of the nucleus is not invariable. The occurrence 

 and significance of amitosis have been much debated. 

 Some few biologists hold that amitosis is more widespread 

 among animals, even in the development of eggs, than is 

 generally believed and that it may be of equal significance 

 with mitosis. The majority opinion is that amitosis is of 

 restricted occurrence and when found among multicellular 

 organisms is of little significance generally, except as a sign 

 of decadence or of too highly specialized cells. ^ For the 



Protista we meet the view that what is often called amitosis 

 is a disguised mitosis. Nevertheless, it is generally 

 admitted that among both multicellular and unicellular 

 organisms amitosis does occur. It must, therefore, be 

 embraced by any theory that attempts an explanation of 

 cell-division, especially if the explanation relates division 

 of the cytoplasm to that of the nucleus. 



As has been pointed out already, mitosis or indirect 

 nuclear division involves a series of orderly maneuvers of 



^ Wilson, 192^. 



250 



