232 



Mr. E. J. Bles. On the Openings in the 



effect of mixing equal volumes of hydrogen and helium, each of 

 which has too large a coefficient of elasticity, is to cause each to 

 occupy twice the voiume that they previously occupied, and to halve 

 approximately the pressure for each. The pressure is therefore 

 lower than it would be for an absolutely ideal gas, for each gas, 

 hydrogen and helium. The sum of these pressures will accordingly 

 be too low, or transposing, the sum of the volumes will be too great. 

 The opposite argument holds for air. 



Now, in considering volumes we deal not merely with the co- volume, 

 i.e., the space occupied by the molecules, but also with the inter- 

 stitial space inhabited by the molecules. But the refractive power, 

 if Clausius's deduction from the formula of Lorenz and Lorentz is 

 correct, is a function of the dielectric constant, and hence of the 

 co- volumes of the gases. And here the discrepancy is more easily 

 detected than by any determination of density. It must therefore be 

 concluded that gases are not, as postulated by Dalton, indifferent to 

 one another's presence, but that they modify one another's properties 

 in the same manner as do liquids, though to a different extent. This 

 mutual action at high pressures and small volumes modifies even the 

 volume relations, as recently shown by Dr. Kuenen. And it must 

 persist at low pressures and large volumes, though it may not always 

 be possible to make measurements of pressure and volume accurate 

 enough to lead to its detection. The refractivity, however, seems to 

 be a means delicate enough to be used for this purpose. 



" On the Openings in the Wall of the Body-cavity of Verte- 

 brates." By Edward J. Bles, B.Sc. (Lond.), King's 

 College, Cambridge. Communicated by Dr. Hans Gadow, 

 F.R.S. Received June 16 — Read June 17, 1897. 



In the review of the vertebrates held in the following pages, I have 

 put together as many facts as I could ascertain on the distribution of 

 abdominal pores in the various groups, and side by side with this 

 evidence I have arranged the available facts recorded by others, and 

 observed by myself, on the distribution of nephrostomes and other 

 openings on the wall of the abdominal cavity. 



By so doing, the physiological meaning of the abdominal pores has, 

 I believe, been elucidated through the evidence of a correlation, speak- 

 ing generally, of an alternative character, between these two sets of 

 organs. It will further appear that in most of the higher vertebrates 

 — where abdominal pores do not occur and nephrostomes disappear 

 early in development or lose their original connection with the renal 

 ducts— the body-cavity has taken upon itself a different functional 

 character. Instead of acting as auxiliary to the excretory organs, it 

 takes part in the internal work of the circulatory lymphatic system. 



