THE LOBSTER AS A TYPE OF CRUSTACEA 23 



on the upper surface of the segment. The cavity is 

 lined by a delicate continuation of the chitinous 

 covering of the body, and has on its inner surface a 

 series of feathered hairs of the kind described above, 

 which are richly supplied with nerve-fibres from a 

 large nerve entering the base of the antennule. 

 Within the cavity, and for the most part entangled 

 among these hairs, are a number of grains of sand. 

 When the Lobster moults, the lining membrane of 

 this cavity is thrown off like the rest of the exo- 

 skeleton, and with it the contained sand-grains. 

 While the shell is still soft after moulting, and the 

 lips of the slit are not rigid, as they afterwards 

 become, fresh sand-grains find their way into the 

 cavity to take the place of those which have been 

 cast off. Perhaps, like some other Crustacea, the 

 Lobster buries its head in the sand to insure that 

 some grains may find their way in ; for its pincers 

 are too clumsy for it to pick up sand-grains and to 

 place them in the cavity, as some Prawns have been 

 seen to do. At all events, if a freshly moulted 

 Prawn be placed in a vessel of sea-water, and 

 supplied, instead of sand, with powdered glass or 

 metal filings, particles of glass or metal will after a 

 short time be found in its antennular cavities. This 

 habit has been utilized in a very ingenious experi- 

 ment by which the function of these organs was 

 demonstrated. A Prawn had been induced in this 

 way to place particles of iron filings in the cavities, 



