14 



THE BREEDING OF ANIMALS 



somes of the egg-cell unite with those of the sperm-cell 

 and a new nucleus is thus formed which becomes the 

 active center of the new daughter cell. 



16. The spermatozoon. The male germ-cell or sper- 

 matozoon is exceedingly minute and its investigation cor- 



FIG. 4. Human spermatozoa (greatly magnified), a, acrosome; 

 6, nucleus ; c, end knob ; d, middle piece ; e, tail ; /, end piece ; g, axial 

 filament. 



respondingly difficult. Although early discovered, its 

 significance was not clearly determined until 1865 when 

 Schweigger-Seidel and St. George discovered that the 

 sperm was a cell and contained a nucleus, cytoplasm and 

 all the essential "elements of a perfect cell. The function 

 of the sperm-cell is to fertilize the egg and thus provide 



