FRESH-WATER FISHES— MYERS 341 



surprised to see it finally prevail. However, there is just as weighty 

 authority against it, and since the fishes might be construed as favoring 

 either side of the argument, I shall not now consider it further. 



The bridge builders are those zoogeographers who are prone to 

 postulate vast continental connections, which they beheve existed in 

 what is now the deep sea, in order to provide bridges over which the 

 land faunas could march to destinations to which they obviously got 

 somehow. The more radical of this school frequently sink (in theory) 

 whole halves or quarters of continents to the deep sea and raise vast 

 areas of ocean bottom into new continents to explain their ideas of 

 how Hving things evolved and migrated. Unfortunately, there is 

 little geological evidence for the more bewitching of these schemes, 

 and zoogeographers are coming to depend on them less and less. To 

 my mind, the most sensible of these "bridges" are the narrow and not 

 at all starthng "isthmian links" of Willis (1932) and Schuchert (1932); 

 they have the unique backing of what appears to be sound geological 

 and bathymetric support, and in addition, some of them are still in 

 existence either as true continental connections (Panama) or chains 

 of islands (West Indies). 



Those who do not build bridges are the zoogeographers who, since 

 the time of Wallace, have held sternly and perhaps a httle too tena- 

 ciously to the theory of the "permanence of the ocean basins." They 

 do build bridges, but very modest ones. They hold that, by and 

 large, the only areas that have ever been dry land are those either 

 now dry or a part of the continental shelves, that parts of continents 

 have been flooded but never deeply, that no major portion of the really 

 deep-sea bottom has ever been upraised into dry land, and that the 

 small land bridges they postulate can account for all the migrations 

 of land animals that have occurred. It must be admitted that this 

 school has been the most cautious in examining the available evidence 

 and the most erudite in its researches; of late years it has also been 

 the most stiff-necked in considering contrary opinion. Its foremost 

 recent exponent has been the late W. D. Matthew, whose Chmate and 

 Evolution (1915) has had a profound and overwhelming effect on 

 nearly all recent American vertebrate zoogeographers, and but Httle 

 on anybody else. There is no doubt, however, that Matthew's 

 views deserve the most careful consideration, and it is unfortunate 

 that he did not live to write the proposed enlarged and revised edition 

 of his work.^ 



Matthew's thesis was, briefly, that "secular chmatic change has 

 been an important factor in the evolution of land vertebrates and the 

 principal known cause of their present distribution" and that, in 

 later geological epochs, most continental groups of animals have origi- 

 nated in the great northern land mass of Eurasia and North America 



I For which I had gathered the Ichthyological information. 



