1885.] 227 [Annual Meeting. 



imals as in coral reefs, the action of the winds in destining as 

 well as building up rocks, and other similar topics. It will be 

 noted that in many cases, the complementary action, or results of 

 the action of these forces, will be exhibited in examples of their 

 destructive as well as constructive aspects, placed close together 

 so as to bring out the contrast in an effective manner. 



The section of Dynamical Biology should consist also of two 

 subdivisions ; first, results of the fundamental or purely physical 

 causes of change, and, second, the secondary or organic causes of 

 change. We have in several essays taken the ground, that the 

 selective action of physical forces, which has heretofore been 

 confounded with natural selection, should be entirely separated 

 from the latter, and called physical selection. This is a primitive 

 law by which animals are modified, and those which are suitable 

 and modifiable are selected, and those which are unsuitable, and 

 incapable of modification, become scarcer and finally disappear. 



Natural Selection, as compared with Physical Selection is second- 

 ary and is active only when one animal comes in contact with 

 another during the struggle for existence. The modifications pro- 

 duced by one of these agencies are distinct and separable from 

 those produced by the other, and can, we think, be exhibited 

 by means of properly selected examples. 



The object of the collection is parallel, and at the same time sup- 

 plementary to that of dynamical geology. In this last we shall treat 

 of the mode of action of the agencies which have modified the earth's 

 surface and built up its varied contours, while in the biological 

 series, the object in view will be a clear exposition of the mode 

 of action of the agencies which have controlled the evolution of 

 organisms. 



Physical selection can be shown by following out such topics as 

 the relations of animals and plants to the maximum of heat and 

 the minimum of cold, taking the approximate limits of the success- 

 ful performance of vital functions, and the secondary effects of 

 heat and cold can be exhibited in the more specialized limits of 

 the distribution of forms with relation to temperature in the seas 

 and upon the land. The effects upon animals and plants of 

 the action of gravitation can be illustrated with specimens, such 

 as some shells which become irregular in shape after they become 

 attached, and of the results of experimentation upon plants b}^ Dar- 



