27 
of Edinburgh , Session 1884-85. 
Pactile papillae, over one hundred in number, are found situated 
at intervals along the edge of the mantle skin. They lie in pockets, 
which open on the ventral side of the skirt. They are apparently 
modifications of those found in Haliotis , and may serve as organs 
of locality-sense. 
The observations of Lankester, Bourne, and Cunningham on the 
renal system are confirmed, and in some respects extended. The 
history of the renal epithelium appears to be similar to that stated 
by Yon Jhering, to be characteristic of the cells of the kidney of 
Tethys. The structure and behaviour towards reagents of the 
epithelium of the right and left kidneys is different, and it is 
suggested that the excretion of the two kidneys may be chemically 
distinct. 
The structure of the heart (auricle and ventricle) and blood- 
vessels, and the lacunar system, is discussed. The blood-corpuscles 
are colourless, and amoeboid. Coagula resemble plasmodia of 
Monobia. 
The alimentary, nervous, a'nd reproductive systems are reserved 
for a future paper — the second half of Part I. 
2. A Theory of Solution. By W. W. J. Mcol, M.A., B.Sc. 
(Abstract.) 
This paper contained an account of the experimental evidence in 
support of the theory of solution enunciated in a paper * “ On the 
Nature of Solution,” communicated to the Society in January 1883. 
Solution of a salt in a liquid is a consequence of the attraction 
of the molecules of the liquid, for a molecule of the salt (adhesion), 
exceeding the attraction of the molecules of salt for one another 
(cohesion). As the number of dissolved salt molecules increases, 
the attraction of the molecules of liquid for the molecules of salt 
becomes more and more balanced by the mutual attraction of the 
salt molecules. When these two forces are in equilibrium, saturation 
ensues. 
Increase of solubility with rise of temperature is due to the co- 
hesion of the salt being diminished by heat to a greater extent than 
* Phil. Mag., February 1883 ; see also Proceedings R.S.E., 1880-82; 
Berichte der deut. Chem. Ges . , October 1883. 
