344 PROCEEDINGS OF THE AMERICAN ACADEMY 



To see the connection between the development of life on the several 

 continents and the variety of their outlines, it will be necessary to con- 

 sider, from the point of view of Mr. Darwin, the difference between the 

 conditions in which life is developed on two surfaces of equal area but 

 differing very widely as regards the irregularity of the surfaces. In 

 the first place, the irregularity of any extended land surface is in a 

 general way a good measure of the number of important geological 

 accidents to which the region has been subjected. There can be no 

 question that Europe, the most varied of the continents in external sur- 

 face, has many more distinct mountain systems than North America, 

 the next in our series. Each of these " systems " is the mark of a 

 wide-spread change of physical conditions which has brought important 

 disturbances into the relations of the life by such accidents existing on 

 sea and land. Many species would be extinguished, and, of those which 

 survived, many would have to adapt themselves to new conditions, and 

 so change and advance are made possible. Again, there is a direct and 

 constant influence exercised by diversity of surface. The number of 

 specific forms, and the consequent energy of the struggle for existence 

 on any continent is, other things being equal, dependent upon the va- 

 riety of conditions it offers to life. Compare two equal areas of, say, 

 one hundred miles in extent, the one a level plain, the other thrown 

 into a mountain mass, which extends from the tropics at the base to the 

 frigid zone at its summit of perpetual snow. On the one you may find 

 essentially the same organic forms throughout, and the competition is at 

 the minimum ; on the other, every mile of ascent brings you in contact 

 with new forms, all the conditions of land life are crowded together, 

 and their varied creatures put into such immediate contact that the 

 struggle must be very much intensified. The seeds of plants belong- 

 ing on the different zones, the insects which depend upon them, the 

 many creatures dependent on the plant or insect life, are often swept 

 by the streams or the winds, or forced by want of food into new con- 

 ditions of life ; cross-fertilization of plants and animals is far more likely 

 to take place in these metropolitan centres of life than where the 

 boundaries of species are made by barriers more insuperable than a 

 mile of mountain slope. 



Professor John Trowbridge presented the following remarks 

 on Animal Electricity : — 



The investigations of Du Bois Reymond, Matteuci, and others have 



