12 



THE GERM CELLS: MITOSIS, MATURATION AND FERTILIZATION 



in the uterine tube three and one-half weeks after coitus. They have been kept 

 ahve eight days outside the body by artificial means. It is not known for how 

 long a period they may be capable of fertilizing ova, but, according to Keibel, this 

 period would certainly be more than a week. Lode estimates that 200 million 

 spermatozoa are hberated at an average ejaculation. 



n. ,-■ 



MITOSIS AND AMITOSIS 



Before the discharged ovum can be fertiUzed by the male germ cell, it must 

 undergo a process of cell division and reduction of chromosomes known as matu- 



ration. As the student may 



not be famihar with the proc- 

 esses of cell division, a brief 

 description is appended. (For 

 details of mitosis see text- 

 books of histology and E. B. 

 Wilson's "The CeU.") 



Amitosis. — Cells may di- 

 vide directly by the simple 

 fission of their nuclei and 

 cytoplasm. This rather in- 

 frequent process is called 

 amitosis. Amitosis is said 

 by many to occur only in 

 moribund cells. It is the 

 type of cell division demon- 

 strable in the epithelium of 

 the bladder. 



Mitosis. — In the repro- 

 duction of normally active 

 cells, compHcated changes 

 take place in the nucleus. 

 These changes give rise to 

 thread-like structures, hence 

 the process is termed mitosis 

 (thread) in distinction to 

 amitosis (no thread). Mitosis is divided for convenience into four phases 

 (Fig. 9). 



vn...- 



Fig. 9.— Diagram of the phases of mitosis (Sdiafer). 



