336 



THE INTERNAL ENVIRONMENT OF THE BODY 



Part III 





B 



Fig. 18.3. Photomicrographs of eggs and sperm. /4, human ovum about to burst 

 the enclosing sac and leave the ovary. B, a similar stage of the ovum of a macaque 

 monkey. C, living human ovum washed out of an oviduct and photographed im- 

 mediately. The small whitish spots are fatty particles; the nucleus is not visible. The 

 human ovum is about 1/175 of an inch in diameter, barely visible to the naked eye. 

 D, living human sperm photographed through a phase contrast microscope. The 

 nucleus of the sperm cell contains the substance of 24 chromosomes, half the herit- 

 able material of a new individual. The human sperms are the smallest cells in the 

 body; estimated to take about 2500 of them to cover a period mark such as on this 

 page. (A, B, C, courtesy, Patten: Human Embryology, ed. 2. New York, The 

 Blakiston Co., 1953. D, courtesy, O. W. Richards, American Optical Company.) 



