GENESIS. 219 



h would take too much space here to specify, the one uni- 

 versal peculiarity which it concerns us to remark, is, this co- 

 alescence of a detached portion of one organism, with a more 

 or less detached portion of another. 



Such protophytes as the PalmellcB and the Dcsmidle(Bf 

 which are sometimes distinguished as unicellular plants, show 

 us a coalescence, not of detached portions of two organisms, 

 but of two entire organisms : in the Palmellce, conjugation is 

 a complete fusion of the individuals ; and in the DesmidiecB, 

 the entire contents of the individuals unite to form the germ- 

 mass. Where, as among the Confervcs, we have aggregated 

 cells whose individualities are scarcely at all subordinate to 

 that of the aggregate, the gamogenetic act is effected by the 

 union of the contained granules of two adjacent cells. In 

 Spirogyra, it is not adjacent cells in the same thread which 

 thus combine ; but cells of one thread with those of another. 

 As we ascend to plants of high organization, we find that 

 the two reproductive elements become quite distinct in 

 their characters ; and further, that they arise in different 

 organs set apart for their production : the arrangements 

 being such, that the sperm-cells of one plant combine with 

 the germ-cells of another. 



There is reason to think thdt, among the lowest Protozoa^ 

 a fusion of two individualities, analogous to that which occurs 

 in the conjugation of certain Algce, is the process from which 

 results the germ of a new series of individuals. But in 

 animals formed by the aggregation of units that are homolo- 

 gous with Protozoa, the sperm-cells and germ-cells are differ- 

 entiated. And even in these humble forms, where there is no 

 differentiation of sexes, we have good evidence that, as in all 

 higher forms, the union is not between sperm-cells and germ- 

 cells that have arisen in the same individual ; but between 

 those that have arisen in different individuals. 



The marvellous phenomena initiated by the meeting of 

 sperm-cell and germ-cell, naturally suggest the conception of 

 some quite special and peculiar properties possessed by theot* 



