FEBRUARY 51 



that the same species does not take independent rise in 

 areas remote from each other. Yet this little Galaxids 

 cannot be an immigrant into South America from 

 Australasia, nor vice versa. Thousands of miles of salt 

 water bar the way. The suggestion is obvious that in 

 the Tertiary epoch terrestrial connection existed between 

 South America and Australasia, and that Oalaxias pre- 

 serves unchanged the features of ancestors which existed 

 anterior to the severance of the two continents, and long 

 before the appearance of man upon the earth. Even so, 

 it would be remarkable that individuals of so very plastic 

 a class should have undergone no specific modification in 

 the course of tens of thousands of years of isolation ; and 

 in any case it would be rash, in the absence of geological 

 evidence, to assume a former different distribution of land 

 and ocean in order to account for the presence of Oalaxias 

 in lands so widely separated. 



Coming now to the northern hemisphere, there is to 

 be noticed the presence of several identical species in 

 Europe and North America. The Atlantic salmon, the 

 sturgeon, and the common stickleback have no particular 

 relation to the problem of dispersal, for the first two are 

 regular sea-going species, and the stickleback accom- 

 modates himself readily to salt water. The perch, also, 

 has no aversion for brackish water, though it is not so 

 simple to account for the presence in American waters of 

 the European pike {Esox lucius) alongside of distinctively 

 American and closely allied species such as the mascalonge 

 (Esox estore). But in the burbot (Lota vulgaris) we 

 come to a fish singular in many respects, among others, 

 that it is the only fish of the cod family inhabiting fresh 

 water, and not only so, but absolutely impatient of salt 



