October 11, 1901.] 



SCIENCE. 



563 



all the islands of the tropical Pacific lying 

 to the east of Wallace's line. This line, 

 separating Borneo from Celebes and Bali 

 from Lompoe, marks in the Pacific the 

 western limit of Cyprinoid fishes, as well as 

 that of monkej^s and other important 

 groups of land animals. This line, recog- 

 nized as very important in the distribution 

 of land animals, coincides in general with 

 the ocean current between Celebes and 

 Papua, which is one of the sources of the 

 Kuro Shiwo. 



In Australia, Hawaii and Polynesia gen- 

 erally, the fresh-water fishes are derived 

 from marine types by modification of one 

 sort or another. In no case, so far as I 

 know, in any island to the eastward of 

 Borneo, is found any species derived from 

 fresh-water families of either the Eastern 

 or the Western Continent. Of course, 

 minor subdivisions in these districts are 

 formed by the contour lines of river basins. 

 The fishes of the Nile differ from those of 

 the j^iger or the Congo, or of the streams 

 of Madagascar or Cape Colony, but in all 

 these regions the essential character of the 

 fish fauna remains the same. 



SOUTHERN ZONE. 



The third great region, the Southern 

 Zone, is scantily supplied with fresh-water 

 fishes, and the few it possesses are chiefly 

 derived from modifications of the marine 

 fauna or from the Equatorial Zone to the 

 north. Three districts are recognized, 

 Tasmanian, the New Zealand and the 

 Patagonian. The fact that certain peculiar 

 groups are common to these three regions 

 has attracted the notice of naturalists. 



ORIGIN OF NEW ZEALAND FAUNA. 



In a critical study of the fish fauna of 

 New Zealand,* Dr. Gill discusses the origin 

 of the four genera and seven species of fresh- 

 water fishes found in these islands, the prin- 

 cipal of these genera ( Galaxias) being repre- 



* 'A Comparison of Antipodal Faunte,' 1887. 



sented by nearly related species in South 

 Australia and in Patagonia.* 



According to Dr. Gill, we can account for 

 this anomaly of distribution only by sup- 

 posing, on the one hand, that their ances- 

 tors were carried for long distances in some 

 unnatural manner, as (a) having been car- 

 ried across entombed in ice, or (6) being 

 swept by ocean currents, surviving their 

 long stay in salt water, or else that they 

 were derived (c) from some widely distrib- 

 uted marine type now extinct, its descend- 

 ants restricted to fresh water. 



On the other hand. Dr. Gill suggests that 

 as ' community of type must be the expres- 

 sion of community of origin,' the presence 

 of fishes of long-established fresh-water 

 types must imply continuity or at least con- 

 tiguity of land. The objections raised by 

 geologists to the supposed land connection! 

 of New Zealand and Tasmania do not ap- 

 pear to Dr. Gill insuperable. It is well 

 known, he says, " that the highest mountain 

 chains are of comparatively recent geolog- 

 ical age. It remains, then, to consider 

 which is the more probable, (1) that the 

 types now common in distant regions were 

 distributed in some unnatural manner, by 

 the means referred to ; or (2) that they are 

 descendants of forms once wide-ranging 

 over lands now submerged." After con- 

 sidering questions as to change of type in 

 other groups. Dr. Gill is inclined to postu- 

 late, from the occurrence of species of the 

 trout-like genus Galaxias, in New Zealand, 

 South Australia and South America, that 

 " there existed some terrestrial passage-way 

 between the several regions at a time as late 

 as the close of the Mesozoic period. The 

 evidence of such a connection afforded by 

 congeneric fishes is fortified by analogous 

 representatives among insects, mollusca and 

 even amphibians. The separation of the 

 several areas must have occurred little later 

 than the late Tertiary, inasmuch as the salt- 



* Galaxias, Neochanna, Prototroctes and Betropinna. 



