CHAPTER XXII 



HOW ORGANISMS REPRODUCE THEMSELVES 



Since genetics concerns itself, among other things, with the fact 

 that certain characters of parents or grandparents are repeated in their 

 progeny, part of the proper field of this science is the study of the 

 details of reproductive processes and procedures. We can actually 

 observe the production of new individuals as the result of the isolation 

 of some representative part of a parent and the reappearance out of 

 such a part of the characteristic structures of the parent or of the race 

 of which the parent is one representative. There is a material con- 

 tinuity between the two successive generations, and we have never 

 known of a case of the origin of a new individual except from a part 

 of a previously existing individual. The chief problem of genetics is 

 to explain exactly how a small piece of a parent can carry all of the 

 characteristics of the race and many of the peculiarities of the indi- 

 vidual parents, and how the material representatives of racial and indi- 

 vidual characters come to express themselves in the offspring. 



By way of introduction to a study of heredity, it should be pointed 

 out that there is a continuity of Ufe through the ages and that this 

 continuity is essentially cyclical or rhythmic in character. Individual 

 life cannot go on indefinitely, for individuals either die or pass on by 

 division into offspring. Even in the simplest organisms individual life 

 comes to an end, and life must be carried on by successive individuals. 

 There is a sort of pulse of racial life which runs from youth to maturity, 

 to senescence, and then back to youth. There is a starting over of 

 individual development with each new generation, and this starting 

 over is the phenomenon of reproduction. 



REPRODUCTIVE PROCESSES 



In this discussion we shall for the sake of clearness limit ourselves 

 to reproduction among the multicellular organisms, though there is 

 probably no essential difference in matters of reproduction between 

 the Protozoa and the Metazoa. 



E. B. Wilson,' in his new momumental work, The Cell in Develop- 



• Edmund B. Wilson, The Cell in Development and Ueredily (1925). 



299 



