420 OEIGIN OF LIFE IN AMEEICA 



arisen partly by accidental dispersal and partly by migration 

 through the existing continents, when they were united by 

 short temporary land bridges in the far north. 



Sir Joseph Hooker seems to have been the first to formulate 

 the theory of a former land connection of southern lands from 

 the occurrence of identical species of plants in widely 

 separated areas. The first to mention an antarctic continent 

 in this connection was Professor Euetimeyer. This was 

 twenty years later, in 1867. Six years elapsed after that until 

 Professor P. W. Hutton again brought forward the theory, 

 expressing his belief in the former existence of an antarctic 

 land-mass and its union with the southern extremities of the 

 present continents. A few years later Dr. Gill declared him- 

 self in favour of a large continental mass embracing Africa, 

 South America and Australia, his views being based on the 

 geographical distribution of fishes. The fact that Dr. Wallace 

 repudiated the opinions expressed by his predecessors need 

 not be taken too seriously. Since his great work on the geo- 

 graphical distribution of animals was issued, facts have been 

 brought to light which are so overwhelmingly in favour of 

 some kind of continuous land connection between South 

 America and the Australian region that he could not at the 

 present day assert, as he did then, that the affinities alluded to 

 are mostly due to accidental dispersal across the ocean, aided 

 by the presence of an antarctic land-mass unattached to other 

 continents. Professor Hutton subsequently abandoned his 

 theory of a land-bridge between the two regions by way of an 

 antarctic continent in favour of a land connection right across 

 the South Pacific towards the end of the Mesozoic Era.* 



In the year 1891, an important contribution to the subject 

 was published by Dr. von Ihering.f He points out that the 

 species of fresh-water Unio from New Zealand and adjoining 

 countries have their nearest allies exclusively in Chile and 

 southern Brazil, and that the fresh-water crayfishes (Para- 

 stacidae) show the same character. The conclusions he de- 

 rives from these and other facts are that the southern portions 



* Ortmann, A. E., " Origin of Antarctic Faunas and Floras," pp. 139 — 

 140. 



t Ihering, H. von, " Eelations between New Zealand and South 

 America," p. 442. 



