161 VIGNETTES FROM INVISIBLE LIFE. 



There is here no decay or dissolution ; the new 

 life and the old are blended and carried forward in 

 the increased number of individuals ; and if this 

 process could be maintained adinfinitum it is evident 

 they would never die, but would fill the universe 

 with their ever-increasing numbers. 



Amazing numbers are indeed produced in this 

 way, for although the process of self -fission takes 

 about twenty-four hours in each case, yet as long 

 as it lasts it proceeds in a geometrical ratio, 

 and the calculation is, that the progeny of a 

 single Diatom in one month reaches the enormous 

 number of one thousand millions of individuals. 

 But Nature imposes a limit on growth, or 

 cell-multiplication. The favouring season expires, 

 or the exhausting and resting period is reached, 

 decay supervenes, and dissolution ends the indi- 

 vidual life. Before this, however, provision has 

 been made for the recommencement of the life- 

 cycle by another process, which is not that of 

 growth or mere multiplication, but is essentially 

 reproductive. This is by conjugation, or the union 

 of the contents of two cells. Two Diatoms are 

 seen to approach each other, and after a time 



