564 



SCIENCE. 



[N. S. Vol. XIV. No. 354. 



water fishes of corresponding isotherms 

 found along the coast of the now widely- 

 separated lands are to such a large extent 

 specifically different. In general, change 

 seems to have taken place more rapidly 

 among marine animals than fresh-water 

 representatives of the same class." 



It is not often that I have occasion to 

 differ from Dr. Gill on a question in ich- 

 thyology ; but, in this case, when one guess is 

 set against another, it seems to me that the 

 hypothesis first suggested, rather than the 

 other, lies in the line of least logical resist- 

 ance. I think it better to adopt provision- 

 ally some theory not involving the existence 

 of a South Pacific Antarctic Continent, to 

 account for the distribution of Galaxias. 

 For this view I may give five reasons : 



1. There are many other cases of the sort 

 equally remarkable and equally hard to ex- 

 plain. Among these is the presence of 

 species of paddle- fish and shovel -nosed 

 sturgeon,* types characteristic of the Mis- 

 sissippi Valley, in Central Asia. The pres- 

 ence of one and only one of the five or six 

 American species of pike f in Europe ; of 

 one of the three species of mud-minnow in 

 Austria , | the others being American. Such 

 cases occur all over the globe and must be 

 explained, if at all, on some hj^pothesis other 

 than that of former land connection. 



2. The supposed continental extension 

 should show permanent traces in greater 

 similarity in the present fauna, both of 

 rivers and of sea. The other fresh- water 

 genera of the regions in question are differ- 

 ent, and the marine fishes are more differ- 

 ent than they could be if we imagine an 

 ancient shore connection. If New Zealand 

 and Patagonia were once united other 

 genera than Galaxias would be left to 

 show it. 



* Seaphirynchus (the shovel-nosed sturgeon) and the 

 paddle-fish {Polyodon and Psepliurus). 

 f Esox lucius. 

 X Umbra, the mud-ininnow. 



3. We know nothing of the power of 

 Galaxias to survive submergence in salt 

 water, if carried in a marine current. As 

 already noticed, I have found young and 

 old in abundance of the commonest of 

 Japanese fresh-water fishes in the open sea, 

 at a distance from any river. Thus far 

 this species, the hakone * dace, has not 

 been recorded outside of Japan, but it 

 might well be swept to Korea or China. 

 Two fresh-water fishes of Japanese origin 

 now inhabit the island of Tsushima in the 

 Straits of Korea. 



4. The fresh-water fishes of Polynesia 

 show a remarkably wide distribution and 

 are doubtless carried alive in currents. 

 One river-goby f ranges from Hawaii to the 

 Riu Kiu Islands. Another species, | orig- 

 inally perhaps from Brazil through Mexico, 

 shows an equally broad distribution. 



5. We know that Galaxias with its rela- 

 tives must have been derived from a marine 

 type. It has no afiinity with any of the 

 fresh-water families of either continent, un- 

 less it be with the SalmonidiB. The origi- 

 nal type of this group was marine, and 

 most of the larger species still live in the 

 sea, ascending streams only to spawn. 



When the investigations of geologists 

 show reason for believing in radical changes 

 in the forms of continents, we may accept 

 their conclusions. Meanwhile, almost 

 every case of anomalies in the distribution 

 of fishes admits of a possible explanation 

 through ' the slow action of existing causes.' 

 Geologists will attach more weight to bio- 

 logical data, if biologists refrain from in- 

 sisting on theories which at the best are 

 mere possible explanations, in the incom- 

 plete state of our knowledge. 



Finally, I may repeat that real causes 

 are always simple when they are once 

 known. All anomalies in distribution 



* Leuciscus JiaJcuensis. 



\ Eleotris fusca. 



X Awaous crassilabris. 



