Maech 6, 1896.] 



SCIENCE. 



365 



b. Antarctic-cireumpolar subregion. 



The Pelagial of the Indo-pacific Region is 

 completely isolated from that of the Atlantic 

 Region by the notal-circumpolar subregion. 



The fifth chapter is a very important one; it 

 discusses the influence of the earth's geological 

 changes on the distribution of animals, and the 

 geological change of the climatic, topographical 

 and biological conditions. The present condi- 

 tion of the animal kingdom is the final result 

 of a series of geological changes, and the present 

 distribution is caused by the conditions of 

 former times. We know through paleontology 

 that in former periods animals existed in re- 

 gions in which they are missing to-day; the geo- 

 graphical distribution has, therefore, changed 

 in the course of the earth history. There is no 

 longer any doubt that a change in the distribu- 

 tion of water and land, in the climate and in 

 the biological conditions, has taken place; the 

 question is: how extensive was this change ? 



Climatic changes : The view of Neumayer 

 that even during the Jurassic period three 

 climatic zones existed, an arctic, temperate and 

 equatorial, Ortmann rejects with Heilprin and 

 PfeSer. His view is the following : As far as 

 our present knowledge reaches, we may assume, 

 with certainty, that only during the course of 

 the Tertiary did climatic diiferences develop. 

 The principal point of this differentiation con- 

 sists in the separation of a zone around the 

 poles, in which the seasons of the year under- 

 went a change in the height of temperature. 

 This change increased until there was a sharp 

 contrast between the new and the original uni- 

 form conditions of temperature which remained 

 towards the equator. Before this climatic sep- 

 aration appeared, certainly in pre-Tertiary 

 time, a uniform tropical climate existed on the 

 earth, and no climatic regions could be devel- 

 oped in relation to the distribution of animals. 



Topographic changes : 



Ortmann is opposed to the theory, especially 

 advocated by Wallace, of the consistency of con- 

 tinents and oceans since the oldest times. It 

 has often been attempted, he says, to recon- 

 struct the continents existing in former geologi- 

 cal periods. The means of doing this consist 

 first in the tectonic method of geology, and 



second in the data from the distribution of ani- 

 mals and plants. I shall not go into detail con- 

 cerning these questions, which have been dis- 

 cussed lately very frequently (Blanford, Yukes- 

 Brown, Ihering, Baur). I fully agree with Ort- 

 mann that the distribution of land and water 

 has very considerably and frequently changed 

 during geological times, and that these changes 

 must have had an enormous effect on the dis- 

 tribution and differentiation of the fauna. The 

 same holds good of the fluvial, the life zones of 

 the fresh water. 



But it is quite different with the marine life- 

 zones. The litoral follows essentially the lines 

 of the continents. All changes affecting the 

 continent affected also the litoral. We are 

 bound to accept for the litoral a topographical 

 continuity existing from the earliest times. 

 Therefore it is best to assume that in Pre-Terti- 

 ary time, before climatic differences existed, the 

 litoral was in complete climatical and topo- 

 graphical continuity; and that there was no 

 possibility of separation into regions according 

 to climatic and topographic differences. With 

 the appearance of the climatic differentiation in 

 the Tertiary the conditions of the litoral changed, 

 and they gradually reached the form in which 

 they appear to-day. At first, however, there ex- 

 isted a considerable diflference from the present 

 conditions, at any rate through one part of the 

 Tertiary times, which had its cause in the na- 

 ture of the circumtropical girdle. There was 

 still a connection between the Atlantic and 

 Pacific, South and North America being still 

 separated. But at the poles the Atlantic and 

 Pacific were already climatically differentiated. 

 There existed also probably a connection be- 

 tween the Mediterranean and Indian Ocean. If 

 this was really so, there were jiresent perhaps 

 from the beginning to the middle of the Tertiary 

 two large groups of tropical litoral; an American 

 and a Mediterranean-Indo-Pacific region. Possi- 

 bly the West African region belonged to the 

 American litoral. 



From this condition the present distribution 

 of the litoral and its regions developed. The 

 Mediterranean was separated from the Indian 

 Ocean and acquired connection with the At- 

 lantic ; the Isthmus of Panama separated the 

 East American from the West American litoral. 



