168 



similitude to an oblique section of the shell of some Mollusca, such 

 as Pinna. 



The author then proceeds to describe in detail and with particularity 

 the form and progressive growth of the several elements of the tooth 

 as they are met with in examining the growing extremity and pro- 

 ceeding from it towards the mature structure, as long as the elements 

 are susceptible of isolation and individual examination. The anatomy 

 of the soldering particles, and their relation to the production of the 

 cavitary structure of the tooth, is specially dwelt upon. The solder- 

 ing particles are supposed to be isolated at first, but as they enlarge 

 they become connected by a thin film from their upper and under 

 faces. This occurs before the final consolidation of the tissue, and 

 before the soldering particles are indissolubly connected with, and 

 themselves indissolubly connect, the contiguous elements of the tooth. 

 At this stage these particles are still susceptible of isolation, and they 

 may be separated en masse, being held in relative position by the 

 films that connect them. The soldering particles and the connecting 

 films thus constitute a tubular system, which has an independent 

 existence before the final consolidation of the tissue, and this tubular 

 system is introduced between, and interpolated among the previously 

 existing elementary parts of the tooth. 



The author concludes by expressing a coincidence of opinion with 

 Dr. Carpenter, that the minute structure of the tooth is essentially of 

 the same nature as that of the shell of the Echinidae generally. 



April 11, 1861. 



Major-General SABINE, R.A., Treasurer and Vice-President, 

 in the Chair. 



The following communications were read : 



I. " On the Motion of a Plate of Metal on an Inclined Plane, 

 when dilated and contracted ; and on the Descent of Gla- 

 ciers." By the Rev. HENRY MOSELEY, M.A., Canon of 

 Bristol, F.R.S., Inst. Sc. Paris Corresp. Received March 



14, 1861. 



(Abstract.) 



The case in which the upper edge of such a plate (supposed rec- 



