THE HORMONES IN HUMAN REPRODUCTION 



studied biology have mastered at least the rudiments of 

 genetics and the lore of the chromosomes. Unfortunately, this 

 important and beautiful science is almost impossible of ex- 

 planation to those who have not seen animal and plant cells 

 through the microscope. Several writers have made brave 

 attempts to do so, and the reader is referred to their books.* 

 For us let it suffice that egg and sperm cell join ; we shall not 

 attempt here to see what goes on within them. 



Meeting of the germ cells. The eggs and sperm cells of such 

 simple and small animals as Hydra are discharged directly 

 into the water, and the sperm cell swims to the egg. As 

 animals become larger and more complicated, the gonads 

 (ovaries and testes) are built more deeply into the body. 

 Some sort of opening or channel to the surface is then pro- 

 vided. The ovaries and testes of sea urchins, for example, 

 open through the shell by small pores. 



When fertilization depends upon the chance meeting of 

 eggs and sperm cells, or upon such uncertain aids as tides 

 and currents, there is obviously a great risk of failure to make 

 contact. To compensate for this, and also for the subsequent 

 high loss of embryos, due to enemies and unfavorable condi- 

 tions, an enormous excess of germ cells is usually produced. 

 There would obviously be greater economy and safety if some 

 arrangement were made to bring the germ cells together or 

 to put them near each other in the first place. A fantastic 

 variety of such arrangements is seen in nature. Animals that 

 are sluggish like the sea urchins and starfish, or actually 

 fixed in position, like most shellfish as well as the sponges, 

 corals and many ascidians (of which the "sea squirts" are 

 examples) are often aided, as we said above, by tides or other 

 currents. In higher plants, which are not only rooted to the 



2 H. G. Wells, Julian S. Huxley and G. P. Wells, The Science of Life, 

 London, 1929; Charles R. Stockard, The Physical Basis of Personality, 

 New York, 1931; Alan F. Guttmacher, Life in the Making, New York, 

 1933; A. M. Scheinfeld and M. D. Schweitzer, You and Heredity, New 

 York, 1939. 



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