THE WAY LIFE BEGINS 57 



Nature's usual method of creating new and serviceable 

 organs is to transform old ones. A simple tube, the oviduct, 

 instead of merely transporting reproductive cells from the 

 central and protected parts of the body to the outside, 

 as with the fish and frogs, has become an abiding place for 

 the young, where development may go on and the compli- 

 cated nervous system and other organs have time to fully 

 mature. 



The reproduction of all animals, from fish to man, is car- 

 ried out by means of very similar organs. Essentially these 

 are: a gland to prepare special reproductive cells in which are 

 placed the growth material, capable, when joined with its 

 opposite, a male or female cell, of building an organism not 

 only like the parents but resembling the species and, more 

 remotely, all of the ancestors that have gone before; a pair 

 of tubes which either pass the reproductive elements at once 

 to the outside, or, as in the female of mammals, retain them 

 during the process of development. 



The means by which the united cells are enabled to grow 

 into an organism varies only in two ways. The earlier way 

 was to supply the egg with building material and to protect 

 it from too great evaporation and injury by gelatinous or 

 shell-like covering, trusting to the heat from some outer 

 source to supply the energy needed for development; the 

 other and later way was to retain the egg within the oviduct 

 and to supply it from moment to moment with the material, 

 moisture, and heat that is needed. 



Finally, sex — maleness and femaleness — is nature's way of 

 so dividing up the difficult work of reproduction that two 

 organisms with their separate streams of heredity may 

 accomplish it more easily and effectively than one. We do 

 not mean to imply that this division of labor in producing 

 young is the only meaning of bi-parental generation. There 

 are other principles involved too technical and remote to the 

 present interest for discussion here. The separate and com- 

 plementary services of the male and the female in caring 

 for the young from the moment of fertilization to that of their 

 independence, remains the most obvious aspects of sex. 



