i THE PROBLEM 5 



tozoa or pollen grains, are known by the general 

 term of gametes, or marrying cells, and the individual 

 formed by the fusion or yoking together of two 

 gametes is spoken of as a zygote. Since a zygote" 

 arises from the yoking together of two separate 

 gametes, the individual so formed must be regarded 

 throughout its life as a double structure in which 

 the components brought in by each of the gametes 

 remain intimately fused in a form of partnership. 

 But when the zygote in its turn comes to form 

 gametes, the partnership is broken and the process 

 is reversed. The component parts of the dual 

 structure are resolved with the formation of a set 

 of single structures, the gametes. 



The life cycle of a species from among the higher 

 plants or animals may be regarded as falling into 

 three periods: (i) a period of isolation in the form 

 of gametes, each a living unit incapable of further 

 development without intimate association with another 

 produced by the opposite sex ; (2) a period of 

 association in which two gametes become yoked 

 together into a zygote, and react upon one another 

 to give rise by a process of cell division to what we 

 ordinarily term an individual with all its various 

 attributes and properties ; and (3) a period of 

 dissociation when the single structured gametes 

 separate out from that portion of the double structured 

 zygote which constitutes its generative gland. What 

 is the relation between gamete and zygote, between 

 zygote and gamete ? how are the properties of the 

 zygote represented in the gamete, and in what 

 manner are they distributed from the one to the 

 other ? these are questions which serve to indicate 



