386 ORTMANN — DISTRIBUTION OF DECAPODS [Aprils, 



The result is : 



I. One large, continuous, continental mass, comprising almost all 

 of the Old and New Worlds. We may call it Holog^ea. It is 

 composed, not only of the Old World, together with North 

 America {Arctogcza of previous authors), but also of South America 

 (Neogcsa of previous authors). 



Separated from it, we have only the following smaller parts of old 

 continental masses: 



II. Australia, which may be regarded as a second continent. 



III. Madagascar, which is merely an island. 



IV. Antarctica, which, on account of the deterioration of the 

 climate, loses its character as a centre for the origin of life. 



Note — -Here we have the greatest continuity of land masses of the 

 earth that ever existed : practically all parts of the world that are 

 important zoogeographical centres were mutually connected, with 

 the exception of two comparatively small sections, Australia and 

 Madagascar, and the barren regions of Antarctica. 1 This union of 

 old centres of radiation had a very important result : we must attribute 

 to it the fact that the distribution of many continental forms of life 

 has been rendered confused, and the difficulty at the present time in 

 tracing the origin of the different groups. Of course, Upper Cre- 

 taceous Mesozonia and other connections of Pre-Miocene times have 

 had their share in effacing many of the original features of distribu- 

 tion, but Late Tertiary Holog&a is the chief cause of uniformity in 

 distribution: in most cases " cosmopolitan " distribution, with the 

 exception of Australia and Madagascar, may safely be referred to 

 these Upper Tertiary conditions. 



e. Recent time. 



The most important changes that brought about the present dis- 

 tribution of the continents is the separation of North America from 

 Asia by Bering Strait, and of North America fro?n Europe. Thus 

 we obtain a recent Zoogeographie division into parts that represent 

 important centres of distribution : 



I. Old World (Europe, Asia, Africa). This agrees partly with 

 Sclater's Arctogcea, except that North America is excluded. We 

 may choose for it the name Eug^ea. 



1 1 think that in Late Tertiary times Antarctica was not so desolate and desti- 

 tute of life as it is now, but there is no doubt that the present character began to 

 develop. 



