GROWTH AND REPRODUCTION 



761 



months afterwards. Radiolaria gradually dried have become active 

 after eleven years, anguilulse after twenty eight years. Corn found 

 in Egyptian mummies is stated to have germinated after thousands 

 of years. 



FIG. 467. DIAGRAMS SHOWING THE ESSENTIAL FACTS OF REDUCTION IN THE MALE. 

 THE SOMATIC NUMBER OF CHROMOSOMES is SUPPOSED TO BE FOUR. (Redrawn 

 from Wilson's " The Cell," etc.) 



A, B, Division of one of the spermatogonia showing full number of chromosomes 

 (four) ; C, primary spermatocyte preparing for division : the chromatin forms two 

 tetrads; D, E, F, first division to form two secondary spermatocytes, each of 

 which receives two dyads; O, H, division of the two secondary spermatocytes 

 to form four spermatids. Each of the latter receives two single chromosomes 

 and a centrosome which passes into the middle piece of the spermatozoon. 



In the development of the multicellular organism on the lines of 

 a division of labour and differentiation of function of the cells, most 

 important was the provision of special cells for the reproduction of the 

 species. Through these cells the organism can, under proper con- 

 ditions, give rise to new individuals, thus perpetuating the race and 

 winning immortality, the remainder of the individual perishing after 

 an allotted span. 



