80 



OUTLINES OF EVOLUTIONARY BIOLOGY 



which the nucleus appears simply to constrict into two or more 

 parts (Fig. 36). This is known as direct or amitotic nuclear division. 



It is frequently met with in 

 degenerating cells and patho- 

 logical tissues, but it is doubtful 

 if it ever occurs (in the higher 

 organisms at any rate) in cells 

 which are destined to undergo 

 long - continued multiplication. 

 We may therefore regard it as 

 a more or less abnormal process 

 with which we have no need to 

 concern ourselves any further. The phenomena of mitosis, on 

 the other hand, are thoroughly normal and practically universal, 

 and, as we shall see later on, they are of the deepest significance 

 from the point of view of the theories of heredity and variation. 



FIG. 36. Amitotic nuclear Division 

 as seen in Cells from the Cavity 

 of the Parapbysis in Spbenodon, 

 X 1000. 



nu. nuclei. 



