EVOLUTION AND DISTRIBUTION OF ANIMALS. 505 



the sun. We have, says Prof. Vogel, to think of these two bodies 

 as surrounded by extensive atmospheres, and that that of the 

 principal body, or Algol itself especially, must possess considerable 

 illuminating power. Under certain* presuppositions, the height of 

 this atmosphere is estimated at 216,000 English miles, and that of 

 the atmosphere of its dark companion at 168,000 miles. The small- 

 est interval between the atmospheres of the two bodies will thus 

 be 1,600,000 English miles, or less than can be found in our solar 

 system. It is not easy, as Prof. Yogel suggests, to conceive two 

 bodies so near of nearly equal size, one of which is in the highest 

 glow of heat, and the other in a condition of far-advanced cooling. 

 But the facts of observation lead to this conclusion, and in science 

 facts constitute the highest and ultimate authority, before which 

 everything must yield. Thus, we learn from the remarkable dis- 

 coveries in Potsdam and Cambridge that the world-order we meet 

 in our solar system does not reign throughout the kingdom of the 

 fixed stars, but that other relations come in which are quite dif- 

 ferent from those under which we live. — Translated for the Popu- 

 lar Science Monthly from Daheim. 



•♦»■»- 



EVOLUTION AND THE DISTRIBUTION OF ANIMALS.* 



By DAVID STARE JORDAN, 



PRESIDENT OF THE UNIVERSITY OF INDIANA. 



II. 



I was lately called to examine a specially interesting problem in 

 geographical distribution, that of the dispersion of fishes in 

 the Yellowstone Park. This region is a high volcanic plateau, 

 formed by the filling of a mountain basin with a vast deposit of 

 lava. The streams of the park are for the most part among the 

 coldest and clearest of the Rocky Mountains, and apparently in 

 every way suitable for the growth of trout. All the hot springs 

 of the great Geyser basin are not sufficient to warm the waters 

 of the Fire-hole River. Yet, with the exception of the Yellow- 

 stone itself, all these streams are destitute of fish-life. A reason 

 for this is apparent in the fact that the plateau is fringed with 

 cataracts which no fish can ascend. Each stream has a canon 

 and waterfall near the point where it exchanges the hard bed of 

 lava for the softer rock below. So the best of trout-streams, for 

 an area of fifteen hundred square miles, are left without trout, 

 because their natural inhabitants can not get to them. 



On the theory that each species occupies those places best 



* An address delivered before the Chicago Institute, in a course on the Testimony of 

 Science in regard to Evolution. 



