i 4 PROBLEMS OF EVOLUTION 



only as are required to make clear what I have to say about 

 evolution. 



The egg before it is fertilised, of course, like other cells, 

 contains a nucleus, and in the process of maturation this under- 



FIG. i. Diagrams illustrating karyokinesis. A, the resting cell ; B, C, D, succes- 

 sive phases in the formation and the arrangement of the chromatin loops and of 

 the nuclear spindle ; E, F, G, separation of the two sets of daughter chromo- 

 somes and their passage towards the poles of the spindle ; H, I, division of the 

 cell body and formation of the two new nuclei ; c, centrosome ; ckr, chromatin ; 

 c//, cell plate ; HU, nucleoli ; num, nuclear membrane ; s, astrosphere ; sp, 

 spindle. (From Parker's Biology, after Fleming, Rabl, etc.). 



goes elaborate changes. The nucleus divides twice. Now, 

 there are two kinds of cell-dividing, one simple in which 

 the nucleus merely separates into two equal parts, the other 

 extremely complicated. This complicated method bears the 



