CHAPTER II 

 THE PLACE OF FERTILIZATION IN THE LIFE-HISTORY 



Fertilization is essentially the phenomenon of the 

 union of two cells known as gametes to form a single 

 cell known as the zygote. Considered in this broad 

 sense, it is practically a universal phenomenon among 

 animals and plants. The formation and union of gametes 

 probably always goes hand in hand with sex, even in 

 those cases among the Protista when the gametes have 

 not yet been shown to be sexually differentiated. 



There is perhaps no phenomenon in the field of 

 biology that touches so many fundamental questions 

 as the union of the germ cells in the act of fertilization; 

 in this supreme event all the strands of the webs of two 

 lives are gathered in one knot, from which they diverge 

 again and are re-woven in a new individual life-history. 

 It is the central decisive event in the genesis of all sexually 

 produced animals and plants. Thus from one point of 

 view it envisages the entire problem of sex; from another 

 point of view it constitutes the basis of all development 

 and inheritance. The elements that unite are single 

 cells, each usually incapable, under natural conditions, 

 of continued existence or development — on the point of 

 death; but by their union a rejuvenated individual is 

 formed which constitutes a link in the eternal procession 

 of life by virtue of its power of reproduction. Thus to 

 consider the antecedents and the consequents of the 

 process of fertilization would be to outline all of biology. 



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