ANIMAL NATURE OF DIATOMEiE. 349 



they live or the vehicles that introduce them, and en- 

 viron, suffocate, and kill the animals or the plants or 

 their tissues : — then only I should denominate this sub- 

 stance a mineral thus associated with an organic being. 

 In the shields of a Diatomean, as v^^ell as in the discs of 

 Acalephse or Gasteropoda, in the epidermis of Crustacea, 

 in the bones of Vertebrata, this so-called inorganic sub- 

 stance is, at least in part, within the same conditions as 

 the albumen or fibrine or any other proteine combination 

 which constitutes the rest of the tissue. In the Diatomeae, 

 as well as in the MoUusca, the solid shield adapts itself 

 to the successively growing dimensions of the animal, as 

 in the Vertebrata the bones grow pari passu with the 

 other tissues. And since this growth has nothing in 

 common with the crystallisation or successive deposition 

 of minerals, we are forced to allow that this manifestation 

 is of necessity comprehended in our idea of life. 



Kiitzing, therefore, when speaking of Diatomeae, ought 

 to have dwelt upon the fact that in these beings silica 

 exceeds the other material elements, and he ought only to 

 have instituted a comparison between the proportion of this 

 substance, and that which is elsewhere met with among 

 the other material combinations proper to organic beings 

 and at the same time common to them with minerals. 

 Perhaps he would have shrunk from this comparison, for 

 the more the second prevail over the first, the less is the 

 manifestation of life. But we are not endeavouring in 

 this place to learn whether a being is more or less easy 

 to be distinguished. A serpent coiled up and an eagle 

 circling the heavens are certainly different in their mani- 

 festation of life, but the one and the other is equally 

 different from a stone. Where life ceases, death takes 

 place ; for these, being opposite states, admit of no tran- 

 sition. 



The other opinion of Kiitzing, which, though foreign 

 to our present subject, we feel bound to oppose, is the 

 one which suggested to him the theory of two vitalities 

 combined together in equilibrio or in inequilibrio. The 



