6Q A, E. Ortmann — Separation^ and its 



It is obvious that in this respect there is an ample field of 

 research left unoccupied. Although the geological develop- 

 ment of many groups of fossil animals in the successive strata 

 has been investigated, no attention is directed to the influence 

 of the conditions of life upon the single forms, and the influ- 

 ence of separation of these conditions upon the differentiation 

 of particular directions of development. The extant investi- 

 gations treat the matter from a mere systematic and phylo- 

 genetic standpoint, referring only to the stratigraphical condi- 

 tions, but the facts of geographical distribution, and especially 

 of bionomic relations, that is to say, the relations to the gen- 

 eral conditions of life, are mostly neglected. Of course, such 

 studies as are desired here are very difficult, especially because the 

 exact synchrony of the zoological facies deposited in different 

 localities is often uncertain ; but it would be very desirable to 

 collect carefully all the facts relating to these questions, in 

 order to secure material for a study of the mutual relations of 

 the different facies in time and space. Thus, I hope, it will 

 be possible, not only to trace particular species in their devel- 

 opment through different zones, but to understand their suc- 

 cessive mutations and differentiations into separate species, at 

 least within smaller periods of the geological history of the 

 earth, and the study of palaeontology may demonstrate, that 

 separation is a continuously acting factor in the formation of 

 species, and may support my opinion, that it is that particular 

 factor which causes the differentiation of species. 



In more recent geological times another factor causing sepa- 

 ration is added : the climatic differentiation of the surface of 

 the earth. I have demonstrated (1. c, p. 40) that this factor 

 most especially effected the breaking up of the old and more 

 or less continuous life-districts into zoogeographical provinces. 

 While the terrestrial and fluvial districts have been character- 

 ized since the beginning of their existence by discontinuity, 

 the continuity of the marine districts has been interrupted in 

 a peculiarly complicated manner since the introduction of 

 climatic changes, which began in the earliest Tertiary period. f 

 For zoogeographical studies I have divided (1. c, p. 45-60) 

 those parts of the earth which are occupied by the oceans into 

 the following regions : 



I. Littoral life- district. 



1. Arctic region. 2. Indo-Pacific region. 8. West 

 American region. 4. East American region. 5. 

 West African region. 6. Antarctic region. 



*In a paper published recently (this Journal, April, 1896) I have demonstrated, 

 that Neumayr's theory of the existence of climatic zones in Jurassic times is 

 without a proper foundation. I may add here, that the same opinion (that cli- 

 matic changes did not begin until the Tertiary time) is set forth recently by 

 Dubois (The climates of the geological past, 1895). 



