172 VIGNETTES FROM INVISIBLE LIFE. 



should expect their growth to be greater and more 

 brilliant in the tropics which is the case ; while in 

 the polar regions their peculiar structure fits them 

 to supply the place of other vegetable life, and 

 makes them of prime importance as an article of 

 food, and natural equilibriating agency. Still, if 

 wholly vegetable, one would hardly expect to find 

 them so abundant under conditions so unfavour- 

 able to vegetation as the Antarctic Ocean. 



What we become actually aware of in this dis- 

 cussion is the fact of their immense importance in 

 the order of nature, for which their peculiar com- 

 bination of both animal and vegetable nature ren- 

 ders them the unique agents they are. 



We might go further, and say that the Diatom 

 is not only a combination of animal and vegetable 

 nature, but that it represents in its structure the 

 mineral kingdom also ; for are not its valves com- 

 posed of silex, or flint, which it can only obtain 

 from the mineral kingdom, and which constitutes 

 the greater part of its bulk, if such a word may be 

 applied to such minute existences. 



In the reproductive process the germs of future 

 generations being secured, the parental cells die, 



