332 



THi: INTERNAL ENVIRONMENT OF THE BODY 



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Part III 



E55 cell 



Tcslia 

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 sperm cem 



Fig. 18.1. Two methods of reproduction. Top, asexual, by which one cell be- 

 comes two or more. A one-celled animal (Trichospherium) dividing into many 

 individuals; the substance of the parent is entirely divided up among the offspring. 

 Bottom, sexual, by which two cells, egg and sperm, unite in one cell, the first of the 

 multicellular body. A male and a female many-celled animal (Hydra) with the 

 respective sex cells. (Courtesy, Corner: The Hormones in Human Reproduction. 

 Princeton, N.J., Princeton University Press, 1942.) 



their pattern is set; neither their form nor function can be changed, and by 

 itself the life span of either kind is short. When they are joined, the resulting 

 cell contains the potentiality for longer life, an extraordinary variety of pat- 

 terns of structure and actions, and unique adjustments. It may bring forth 

 not only the traits of its parents and grandparents but signs of its ancient 

 animal ancestry. Every child is a surprise. 



Beginnings of Sex 



Conjugation. Paramecia and many other protozoans join in a union or 

 conjugation that resembles the mating of multicellular animals. Ordinarily 

 paramecia swim through the water, passing and repassing their neighbors 



