468 M, straus-durckiieim's 



epidermis and dermis, sometimes beneath the last, and is 

 sometimes external, as may be seen in the Libellulidce. 

 The Arachnida exhibits a similar structure. 



In the Onisci, the teguments, from the large quantity of 

 calcareous matter they contain, have become hard and brittle ; 

 the epidermis and dermis are not distinct, and present no 

 trace of fibres ; they are colourless, and only owe their 

 appearance of being coloured to the mucous matter which is 

 internal. The decapod Crustacea in general only differ from 

 the Onisci in having the colouring matter external : in the 

 articulations the colouring matter is wanting, and the epidermis 

 and dermis are distinct. 



At certain epochs, variable according to the species, the 

 articulated animals change their skins, precisely as do the 

 snakes. Those with soft teguments, as the Annelida, only 

 renew the epidermis, whilst those whose teguments are solid 

 renew also the dermis. The internal prolongations of the 

 dermis, from their situation, cannot be renewed in this manner ; 

 the calcareous matter is, therefore, merely absorbed at the 

 time of the change, and re-deposited after it. 



The teguments of articulated animals differ much from those 

 of the Vertcbrata in their component parts ; they even differ 

 in the different families. 



According to the analysis of M. Odier, the elytra of Melo- 

 lontha vulgaris consists of albumen, an extractive matter, solu- 

 ble in water ; a brown animal substance, soluble in a solution 

 of potass, but not in alcohol ; a coloured oil, soluble in alcohol; 

 a peculiar matter (chitine), forming one-fourth of their weight ; 

 sub-carbonate of potass ; phosphate of lime ; and phosphate of 

 iron. Chitine is insoluble in potass, is soluble in hot sulphuric 

 acid, does not turn yellow with nitric acid, burns without 

 melting, and does not contain azote. 



The teguments of the common crab {Cancer pagurus) are 

 composed of 



Chlorure of sodium and salts of soda ... 1*6 



Phosphate of lime 6*0 



Phosphate of magnesia 1 '0 



Carbonate of lime 62*8 



Water and animal matter 28-6 



100-0 



