2 (-2 The Geographical Distribution of Fishes 



gascar 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 Avith fresh-water fishes, and the few it pos- 

 sesses are chiefly derived from modifications of the marine 

 fauna or from the Equatorial Zone to the north. Three districts 

 are recognized — Tasmania, New Zealand, and Patagonia. 



Origin of the New Zealand Fauna. — The fact that certain peculiar 

 groups are common to these three regions has attracted the 

 notice of naturalists. 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 principal of these genera (Galaxias) being represented by 

 nearly related species in South Australia, in Patagonia,! the 

 Falkland Islands, and in South Africa. 



According to Dr. Gill, we can account for this anomaly of 

 distribution only by supposing, on the one hand, that their 

 ancestors were carried for long distances in some unnatural 

 manner, as (a) having been carried across entombed in ice, or 

 (b) being swept by ocean currents, surviving their long stay 

 in salt water, or else that they were derived (c) from some 

 widely distributed marine type now extinct, its descendants 

 restricted to fresh water. 



On the other hand. Dr. Gill suggests that as "community of 

 type must be the expression of community of origin," the pres- 

 ence of fishes of long-estatilished fresh-water types must imply 

 continuity or at least contiguity of land. The objections raised 

 by geologists to the supposed land connection of New Zealand 

 and Tasmania do not appear to Dr. Gill insuperable. It is well 

 known, he says, "that the highest mountain chains are of com- 

 paratively recent geological age. It remains, then, to consider 

 which is the more probable, (i) 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 

 considering questions as to change of type in other groups, Dr. 

 Gill is inclined to postulate, from the occurrence of species of the 



* " A Comparison of Antipodal Fauna;," 1887. 



■\ Galaxias, Ncochanna, Prototroctes, and Rclropinna. 



