298 GENERAL BIOLOGY 



direct succession, for many of the primary germ cells remain 

 undeveloped through the life of the individual organism, and 

 in most organisms they develop in cycles, corresponding to 



ANTONY VAN LEEUWENHOEK 



(16321723) 



Pioneer microscopist and naturalist; maker of his own 



lenses; discoverer of capillary circulation, of 



sperm cells, etc. 



breeding periods. Division, growth and maturation may 

 often be found side by side in a single reproductive organ. 

 But these external phenomena are mere curiosities of cell 

 behavior, until we inquire what is going on inside the cells. 



