ANIMAL NATURE OF DIATOME^. 505 



we understand the word history in its broadest sense. 

 It must, however, be remembered, that the inorganic 

 crust of the earth contains within it the same elements 

 that enter into the structure of animal and vegetable 

 organs. A physical cosmography would, therefore, be 

 incomplete if it were to omit a consideration of those 

 forms, and of the substances which enter into solid and 

 fluid combinations in organic tissues, under conditions 

 which, from our ignorance of their actual nature, we 

 designate by the vague term of vital forces, and group 

 into various systems in accordance with more or less 

 perfectly conceived analogies. The natural tendency of 

 the human mind, involuntarily prompts us to follow the 

 physical phenomena of the earth through all their varied 

 series until we reach the final stage of the morphological 

 evolution of vegetable forms, and the self-determining 

 power of motion in animal organisms." (Humboldt 

 Cosmos, vol. 1, p. 348. Otte's translation.) 



Page 9. — Nageli appears to me to have treated more 

 profoundly than any other modern author on the limits 

 of the two organic kingdoms, ( Ueber die gegenwartige 

 Aufgabe der Naturgeschichte, inbesondere der Botanik. 

 II, Th. Zeitschr . fiir wissenschaftliche, Botanik. II Heft., 

 1845.) But yet objection may be made as to the 

 differential character established by him, of a cellular 

 membrane, ternary in the vegetable, quaternary in the 

 animal : the primordial utricle of the permanent vegetable 

 cell in the Algae {amylid-cell of Kiitzing), which, like the 

 nucleus to which it is always connected, consists of a 

 quaternary azotised substance, is sometimes, perhaps, not 

 even accompanied by a ternary membrane {gelin-cell of 

 Kiitzing) ; the cellulose itself becomes permeated by nitro- 

 genated matter (Payen, Kiitzing); and finally, an abun- 

 dant ternary substance, isomeric with starch, is present in 

 the organisation of animal beings, (Schmidt, Loewig, 

 KoUiker.) The suggestion of Nageli that the chief 

 cause of animal sensibility and mobility, resides in that 

 characteristic (quaternary, azotised) quality of the cell- 



