OF THE INVERTEBRATE ANIMALS. 41 



b. An internal cavity for the assimilative process. 



c. The ultimate products of the metamorphosis of matter (pro- 

 ducts of the respiratory process). 



d. The substance of the cell-wall. 



Ad a. The Oscillatoriaj and the Spores of the Algee have a 

 spontaneous motion as perfect as, and even considerably more 

 so than, that of the Bacillarice and the fixed marine animals 

 [Ascidice, &c.). This motion is a necessary fundamental con- 

 dition of the physical existence of these beings : what the atmo- 

 sphere is to plants, the ocean is to the adherent marine animals. 

 If the land animals lived in a sea consisting of albumen and 

 hydi-ates of carbon, they would not require a locomotive appa- 

 ratus to enable them merely to replenish their formative matter ; 

 if the atmosphere contained no carbonic acid, plants would stand 

 in need of locomotion. 



Spontaneous motion is the consequence of the presence of the 

 Will. The will without the apparatus requisite for the realization 

 of its ideal activity, would be an extremely useless gift of nature ; 

 and if we adopt the maxim, that " everything in existence is 

 judicious and perfect,^' it would be inadmissible. Cuvier has 

 beautifully treated of the relations of causality in the introduc- 

 tion to his ' Comparative Anatomy.' 



Ad b. What, then, is the principle of this internal cavity in 

 the assimilative process ? Evidently the greatest possible increase 

 of surface so as to favour the most perfect assimilation in an 

 endosmotic apparatus. Do we not perhaps find it realized in 

 plants ? Undoubtedly, the whole system of intercellular spaces, 

 with their outlets in the stomata, exhibits exactly this arrange- 

 ment, except that in their case, preserving the same kind of com- 

 parison, we have the lungs and intestinal tube combined. Car- 

 bonic acid, the formative material of plants, passes freely through 

 the stomata of the elongated canals of the intercellular spaces, so 

 as to be taken up into the surrounding cells by diffusion as for- 

 mative material, just as albumen and the hydrates of carbon pass 

 through the sphincter oris into the intestinal cavity : that which 

 is designated diff'usion in the former corresponds to endosmose 

 in the latter ; the un-named cells of the former constitute the 

 epithelia of the intestinal villi in the latter. 



The Vibrions are usually denominated animals. They exhibit 

 the most active motions ; they permanently exist as simple cells 

 without a trace of contraction even when magnified to the great- 



