92 GENERAL BIOLOGY 



Since the cell gets its food by absorption, it is 

 also of advantage to divide in this way in order 

 to increase the absorptive surface; for whereas 

 solids vary as the cubes of a dimension, surfaces 

 vary only as the squares of a dimension. To use a 

 concrete illustration, the combined surface of two 

 halves of an orange cut in two in the middle is 

 greater than that of the original orange by just the 

 added areas of each cut surface, the cubic content 

 remaining the same. 



Mitosis. The direct cell division just described, 

 in which the nucleus simply cuts in two and the two 

 halves move apart while the cytoplasm cleaves 

 between them to form two new cells, is sometimes 

 observed, but is by no means the usual method. It 

 will be remembered that the content of a cell is 

 normally very heterogeneous, so that a division 

 plane passed through the middle would result in 

 producing two dissimilar halves, and if this were 

 repeated a number of times, the various elements of 

 nucleus and cytoplasm being segregated each time, 

 the resulting cells would soon lose all real resemblance 

 to one another, and the tissue which they compose 

 would lose its homogeneous character. We know 

 that this does not happen. Instead of this direct 

 method of division we find that another sort of cell 

 cleavage usually takes place, to which the name 

 of mitosis 1 has been given. This process is an 

 extremely complicated one, and it will be more 



1 The direct cell division just described is called amitosis. 



