THE CELL 245 
female respectively, according to the sex of the parent 
from which each is derived. In animals the female 
gamete is known as the ovum, and the male as the 
spermatazoon, and the product of their fusion, as already 
said, is called the fertilized ovum. Germ-cells of a 
similar kind arise in a slightly different way in plants. 
The germ-cells are produced in special parts of the 
organism known as the generative organs, which in 
flowering plants are represented by the pistils and 
stamens. 
A more convenient expression for the fertilized ovum 
is that of zygote, a term which we have previously 
encountered in fhe shape of the homo- and hetero- 
zygotes of the Mendelian. By an expansion of meaning 
the term zygote is also used to express the whole 
organism which ultimately arises from the product of 
fusion of a pair of gametes, and by this use the impor- 
tance of the gamete, as opposed to the zygotic organism 
as a whole, is brought into due prominence. 
We find, then, that the succession of generations in 
the higher animals and plants, according to the common 
use of this expression, depends upon the succession 
of a much larger number of cell-generations. By 
repeated divisions, each giving rise to a new generation 
of cells, the fertilized ovum gradually develops into 
the adult organism. By the division of certain 
members of the later generations of cells which compose 
this organism the gametes are produced. By the 
conjugation of a pair of gametes a zygote of the 
second generation arises, and the same processes are 
continually repeated. 
