The Cellular Basis 



137 



FIG. 43. FERTILIZATION OF THE EGG OF THE NEMATODE WORM Ascaris 

 megalocephala. %N, Egg nucleus. $N, Sperm nucleus. Arch, Archiplasm. 

 C, Centrosome. A, B, Approach of germ nuclei. C, D, Formation of two 

 chromosomes in each germ nucleus. E. F, Stages in the division of the 

 chromosomes which are split in E and are separating in F ; only three 

 of the four chromosome pairs are shown in F'. (From Wilson after 

 Boveri.) 



