Proceedings. 315 



1. The crowns of teeth are fully formed before they are erupted, hence 

 cannot come under the law of use and disuse, which is the central idea of 

 the Lamarckian school. 



2. Anatomically they are so constructed as to resist impact to the very 

 best advantage; consisting, as they do, of a hollow tube (pulp canal or can- 

 als) the walls of which are made up of a series of tubes (dental tubuli) 

 standing at right angles to the centiral tube, and these in turn, in the crown, 

 being surmounted by solid prisms (enamel prisms) in such manner that 

 every part of the surface presents the form of an arch with the springers 

 resting upon the hollow columns of the dentine. In addition to the above 

 the surface is highly polished, making an ideal structure to resist im- 

 pact. 



3. The roots of the teeth are covered by a soft membrane which serves 

 as a cushion during the process of mastication and thus relieves the force 

 of impact. 



4. That these same roots are imbedded in cancellated bone which 

 would yield to the force of irhpact before the crowns. 



5. That enamel is a non-vital coat of mail which, when the tooth 

 erupts, is carried away from its source of development and hence cannot be 

 renewed or repaired when injured. 



6. A tooth crown once erupted is subject only to two forms of changes, 

 mechanical abrasion or chemical erosion. 



7. That change in form due to either of these two causes is not sub- 

 ject to inheritance. 



Louis F. Menage was elected to the committee of the Acad- 

 emy for conference with the Library Board in the place of H. L. 

 Gordon. 



The following gifts to the museum from President Hatch, 

 were received : 



1. A series of Unio and Anadonta shells from lake Pepin 

 and vicinity, said to be the first series ever collected in Minnesota. 



2. A specimen of silicified wood from Montana. 

 The secretary was directed to acknowledge the gifts. 



December 8, I89I. 



Twenty-one persons present. 



James E. Bradford and Julius Hortvet were elected mem- 

 bers. 



The following papers were read by title: 'The range and 

 distribution of the Lower Silurian fauna of Minnesota, with 

 descriptions of some new species." F. W. Sardeson. 



"Observations on some American Rhizobia." Dr. A. 

 Schneider. 



