218 



ing, as they do, a communication between the external surface and the 

 nervous structure within, they communicate impressions, and are in 

 fact tactile organs. 



The author had satisfied himself, before the appearance of Dr. 

 Hackel's paper, that the hairs were connected with the inner layers 

 of the corium, and not with the chitinogenous membrane only ; and he 

 had seen indications in the lobster and larger Crustacea of an arrange- 

 ment of the pulp corresponding to the arrangement of the hairs. 

 In the smaller Crustacea, especially in the shrimps, he found a re- 

 markable confirmation of his views. In the flabelliform processes, 

 and even in the claws in these animals, he found that the structures 

 within the shell were arranged in the form of tubes corresponding to 

 the hairs, through which passed from the deeper parts, fibres which 

 were prolonged into the hair-canals. In the claw the nerve was 

 traced to the inner termination of these tubes. The tubes in some 

 instances merged internally into the general mass of the corium ; in 

 others they were truncated. Externally, or towards the margins, they 

 presented open orifices, through which the fibres passed. The fibres, 

 when drawn out from the hair-canals, often presented the plumose or 

 serrated character, according to the form of hair to which they 

 belonged. They could be traced for some distance down the tubes, 

 and at times completely through them, but their deep connexions 

 could not be clearly made out. Several modifications of this arrange- 

 ment are described and figured. The author believes that the facts 

 brought forward are sufficient to establish that the hairs of the Crus- 

 tacea are probably organs by which external impressions are com- 

 municated to the internal sensitive parts. 



III. " Note on the Measurement of Gases in Analysis." By 

 A. W. WILLIAMSON, Ph.D., F.R.S., Professor of Chemistry 

 in University College, and W. J. RUSSELL, Ph.D. Com- 

 municated by Dr. WILLIAMSON. Received April 6, 1858. 



In Bunsen's admirable method of gas analysis, considerable time 

 and trouble are expended in observing the exact temperature and 

 pressure to which the gas is subjected at the time of measurement ; 

 and also in calculating from these data the volume which the gas 

 would occupy at the normal temperature and pressure. Frankland's 



