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hairs with canals penetrating the whole thickness of the shell, and 

 the occasional continuity of the matter which filled the hairs with 

 that which exists in the corresponding canal of the shell. M. Hollard 

 says that the canals of the shell which correspond to the hairs, are 

 occupied by membranous investments, which embrace the base of the 

 hairs, and seem to receive an extension of the nutrient system. He 

 suggests that amongst other functions, the hairs may possibly be con- 

 nected with that of general sensibility. Dr. Hackel in a recent pub- 

 lication has shown that the canals of the shell and hair are lined by a 

 continuation of the outer layer of the soft internal integument, which 

 he calls the chitinogenous layer. He describes minutely the structure 

 of the inner integument, and his account on the whole agrees with 

 that given by Milne-Edwards ; but he does not recognize the presence 

 in the canals, of any of the elements of the inner integument except 

 the external cuticular or chitinogenous layer ; nor the connexion of 

 these canals with the corium which lies beneath it, and which 

 receives abundantly nerves and vessels. 



According to the investigations of the author, it is with this deeper, 

 vascular and nervous layer that the contents of the hair-canals and 

 of the corresponding canals in the shell are especially connected. 

 This can be readily seen in parts where the shell is thin, as in the foot- 

 jaws for example. In a section made in such a situation, the canals 

 leading to the hairs will be found to be often nearly as large as the 

 bases of the hairs to which they correspond. They are lined by a 

 thick membrane, which invests the cup-shaped cavity in which the 

 hairs are implanted, and becomes so closely connected with the bulb 

 of the hair itself, that it is often dragged out with it when the hair 

 is pulled out. The cells and other elements of the deeper layer 

 of the internal integument fill up the canal and pass on into the 

 hairs. 



Where the shell is thick, as in the claw of a lobster, the sheaths 

 which are connected with the hair-bulbs and line the shell-canals can 

 be demonstrated in the mariner adopted by Mr. Tomes to show the 

 existence of the dentinal fibres. If a section of a part of the shell of 

 the claw where the hairs are implanted, and which has been previously 

 softened in dilute acid, be torn through, the'sheaths will usually be 

 dragged out, and will be seen projecting from the torn edges, their 

 contents often remaining in them. The connexion of the inner in- 



