I THE PROBLEM 5 



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 zygfote. Since a zygote arises from the 

 yoking together of two separate gametes, the indi- 

 vidual 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 struc- 

 tures, 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 



