GENESIS. 279 



always the containing cells, often called gametes, are unlike : 

 the sperm-cell being the male product, and the germ-cell the 

 female. But among some Protozoa and many of the lower 

 Alga and Fungi, the uniting cells show no differentiation. 

 Sexuality is only nascent. 



There are very many modes and modifications of modes in 

 which these cells are produced; very many modes and 

 modifications of modes by which they are brought into 

 contact; and very many modes and modifications of modes 

 by which the resulting fertilized germs have secured to them 

 the fit conditions for their development. But passing over 

 these divergent and re-divergent kinds of sexual multiplica- 

 tion, which it would take too much space here to specify, the 

 one universal trait is this coalescence of a detached portion 

 of one organism with a more or less detached portion of 

 another. 



Such simple Algce as the Desmidiece, which are sometimes 

 called unicellular plants, show us a coalescence, not of de- 

 tached portions of two organisms, but of two entire organ- 

 isms: the entire contents of the individuals uniting to form 

 the germ-mass. Where, as among the Confervoidece, we have 

 aggregated cells whose individualities are scarcely at all 

 subordinate to that of the aggregate, the gamogenetic act is 

 often effected by the union " of separate motile protoplasmic 

 masses produced by the division of the contents of any cell 

 of the aggregate. These free-swimming masses of proto- 

 plasm, which are quite similar to (but generally smaller 

 than) the agamogenetic ' zoospores ' of the same plants, and 

 to the free-swimming individuals of many Protophyta, are 

 apparently the primitive type of gametes (conjugating cells) ; 

 but it is noteworthy that such a gamete nearly always unites 

 with one derived from another cell or from another indivi- 

 dual. The same fact holds with regard to the gametes of the 

 Protophytes themselves, which are formed in the same way 

 from the single cell of the mother individual. In the higher 

 types of Conferroidece, and in Vaucheria, we find these equi- 



