REPRODUCTION IN MAN 87 



tlve is to understand each one and recognize the 

 part that it plays in our life. 



Reproduction in man is identical with the same 

 process in animals. The cells which give rise to 

 new human beings are the germ cells, sperms and 

 ova. These differ greatly in size. (Figs. 28-29.) 

 It has been estimated recently that the volume of 

 the human sperm is not over 50 cubic micra (a 

 micron is i/iooQ of a millimeter), while that of 

 the human ovum is 1,767,150 cubic micra, or over 

 35,000 times the volume of the sperm cell. 



The human ova are grown in the two ovaries 

 which contain approximately 72,000 ova at 

 puberty. Each one is a minute, spherical body 

 with a diameter of 1/5 of a millimeter (about 

 1/125 of an inch). It has the typical nucleus sur- 

 rounded by granular cytoplasm. 



The human sperm cell is a minute, elongated 

 whip-lilce cell with one end enlarged. Sperms 

 average about 1/20 of a millimeter in length 

 (about 1/500 of an inch). The large end con- 

 tains the nucleus. 



Sperms are grown in the two spermaries (testi- 

 cles or testes). There is no way of determining 

 accurately just how many sperms a single spermary 

 contains as new ones are continually being formed 

 in some men, from the period of adolescence to 

 old age. Professor G. H. Parker of Harvard 



