504 ANIMAL NATURE OF DIATOME^E. 



especially Professor Rokitansky, hypertrophy of the 

 papillae is detected beneath the condensed epidermis, in 

 inveterate ichthyosis, and in common warts. All accu- 

 mulations of epidermis which assume the form of scales, 

 spring from papillae developed in the form of cylinders, 

 villi, and rami. According to Cruveilhier, accidental 

 horn is a morbid product of papillae of the skin, crowded 

 together, and twisted into a papillary substance. But 

 with regard to hairs growing physiologically and patho- 

 logically, as well as to horn, which seems always to be 

 formed by an agglutination of the skin, we must remem- 

 ber that, as they are composed of two different elements, 

 one an external envelope of epidermic nature, and the 

 other, an oily medulla, varying in colour, so both the 

 papillae and the follicles concur in their formation. Both 

 the one and the other are altered in different ways, 

 precisely according to their accidental, or pathological 

 production." 



As to the organisation of bone, there still remains a 

 doubt with respect to the presence of saline particles 

 mineralogically deposited in the parietes of the bone-cor- 

 puscles ; yet it is proved, that in the numerous concentric 

 laminae that constitute the walls of bone canals, in the 

 radiating tubes that traverse them, and in the bone-cor- 

 puscles themselves, the calcareous substance is in the same 

 condition as the proteine, with which it is found intimately 

 united. 



Recent observations have proved, what might reason- 

 ably be supposed, as to the shells of Mollusca, that they 

 have a decidedly cellular structure, the lime, together with 

 proteine, constituting the walls of the cells. 



We know that the same is true of the silex in the 

 epidermis of Gramineae and Equisetaceae, and of the 

 lime in Corallines and other marine Algae. 



Page 8. " A cosmical history of the universe, resting 

 upon facts as its basis, has, from the nature and limita- 

 tions of its sphere, necessarily no connection with the 

 obscure domain embraced by a history of organisms, if 



