219 
of Edinburgh, Session 1880-81. 
during next winter by operating on water at about 39° F. In tbis 
case there should be no change of temperature unless the maximum 
density point is altered by pressure. 
Monday, 6th June 1881. 
Professor Sir WYY1LLE THOMSON, Vice-President, 
in the Chair. 
The following Communications were read : — 
1. On the Structure of the Skeleton of Tubipora musica, and 
on the Eelation of the Genus Tubipora to Syringopora. 
By H. Alleyne Nicholson, M.D., D.Sc. 
The object of the present communication is to briefly consider 
the general and minute structure of the corallum of the recent 
Tubipora musica , with special reference to the association of the 
genus Tubipora ; with the extinct genus Syringopora , as advocated 
by many modern naturalists. The method of inquiry that I have 
pursued in carrying out this investigation has been principally that 
of preparing similar thin and transparent sections of both the recent 
and the extinct types ; and though there are special difficulties in 
the way of any examination of Tubipora by this method, I have 
been able to overcome these in a satisfactory manner, and to prepare 
a number of thin sections which answer all the requirements of the 
case. The results of my observations may be conveniently con- 
sidered under the following heads : — 
1. General structure of the corallum of Tubipora. 
2. Minute structure of the corallum of Tubipora. 
3. General structure of the corallum of Syringopora. 
4. Minute structure of the corallum of Syringopora. 
5. Supposed relationships between Tubipora and Syringopora. 
1. General structure of the corallum of Tubipora . — The corallum 
of Tubipora musica , Linn., is one so familiar to naturalists that the 
peculiarities of its external form hardly need to be noticed. It 
consists of a number of fasciculate cylindrical tubes or thecae, which 
are separated by small intervals from one another, and are upon the 
