26 Geographical Distribution of Animals. 



Sea. From the Caspian they ascend the Wolga in immense shoals, 

 and are found further east in the lakes of Central Asia, even as far 

 as the borders of China. The great Canadian lakes constitute 

 another centre of distribution of these fishes in the New World, but 

 here they are not so numerous, nor do they ever occur in contact 

 with salt water in this basin. 



Northwards, there is another great zone of distribution of stur- 

 geons, which inhabit all the great northern rivers emptying into the 

 Arctic Sea, in Asia as well as in America. They occur equally in 

 the intervening seas, being found on the shores of Norway and 

 Sweden, in the Baltic and North Seas, as well as in the Atlantic 

 Ocean, from which they ascend the northern rivers of Germany, as 

 well as those of Holland, France, and Great Britain. Even the 

 Mediterranean and the Adriatic have their sturgeons, though few in 

 number. There are also some on the Atlantic shores of North 

 America, along the British possessions as well as the northern and 

 middle United States. They seem to be exceedingly numerous in 

 the Northern Pacific, being .found everywhere from Behring's 

 Straits and Japan to the northern shores of China, and on the north- 

 west coast of America, as far south as the Columbia River. Again, 

 the so-called western waters of the United States have their own 

 species, from the Ohio down to the lower portion of the Mississippi, 

 but it does not appear that these species ascend the rivers from the 

 Gulf of Mexico. I suppose them to be rather entirely fluviatile, like 

 those of the great Canadian lakes. 



Beyond the above limits southwards there are nowhere sturgeons 

 to be found, not even in the Nile, though emptying into a sea in 

 which they occur ; and as for the great rivers of Southern Asia and 

 of tropical Africa, not only the sturgeons, but another family is want- 

 ing there, — I mean the family of Goniodonts, which in Central and 

 Southern America takes the place of the sturgeons of the north. 

 Again, all the species in different parts of the world are different. 



It is a most extraordinary fact, which will hereafter throw much 

 light upon the laws of geographical distribution of animals and their 

 mode of association, viz., that certain families are entirely circum- 

 scribed within comparatively narrow limits, and that their special 

 location has an unquestionable reference to the location of other 

 animals ; or, in other words, that natural families, apparently little 

 related to each other, are confined to different parts of the world, 

 but are linked together by some intermediate form, which itself is 

 located in the intermediate track between the two extremes. In the 

 case now before us, we have the sturgeons extending all around the 

 world in the northern temperate hemisphere, in its seas as well as in 

 its fresh waters, all closely related to each other. Neither in Asia 

 nor in Africa is there an aberrant form of that type, or any repre- 

 sentative type in the warmer zones ; but in North America we have 

 the genus Scaphirhynhus, which occurs in the Ohio and Mississippi, 



