GEOGRAPHICAL DISTRIBUTION, 177 
the one hand, and between those of Eastern North America and of Eastern Asia on the other, 
I have simply made a new application of the theories advanced by Huxley* to explain 
the differences between the crayfishes on the two sides of the equator, and by Asa Gray ¢ 
to account for phenomena in the distribution of plants similar to those presented by the 
crayfishes of the Northern hemisphere. 
The absence of Astacidze over a large part of Asia is well known. None are found in 
the great rivers that flow into the Arctic Ocean, nor in those of the central and southern 
portions of the continent. In connection with the absence of crayfishes from the rivers 
of Southern Asia, Milne Edwards? has suggestively observed that these waters are popu- 
lous with fluviatile crabs of the family Telphusidee. Indeed, as a general rule, crayfishes 
are unknown in regions where fluviatile crabs abound, having succumbed, perhaps, to their 
more highly organized rivals. Huxley remarks, moreover, that if the western Eurasiatic 
cerayfishes are derived from a primitive Aralo-Caspian stock, as seems probable, the great 
Asiatic highlands would form an obstacle to their southward extension into India, while 
the severity of the Siberian winter and the recent submergence of the land beneath the 
ocean are invoked to account for the absence of these animals from the great Asiatic rivers 
that empty into the Arctic Ocean. 
IV. The only islands in the Northern hemisphere known to be inhabited by crayfishes 
lie near the mainland, and the crayfishes contained therein are either the same species as 
those of the adjacent part of the continent, or closely related species. Thus, the species 
found in England and Ireland and in the islands of Cherso and Veglia are the same as 
those of the western and southern parts of Continental Europe, viz. Astacus pallipes. The 
Japanese crayfishes (Cambaroides Japonicus) are nearly related to those of the Amoor 
River (Cambaroides Dauricus and C. Schrenckii), the Cuban species (Cambarus Cubensis) 
to those of Mexico (C. Mexicanus). The chances in favor of accidental transportation of 
animals haying the habits of crayfishes across bodies of salt water such as separate the 
islands in question from the continents are so small, that it seems more probable that 
their distribution was effected through migrations at a former period, when the present 
insulated areas were continuous with the neighboring continents. The connection of the 
British Isles with the continent of Europe in post-glacial times is admitted by geologists. 
Evidence pointing to the former connection of the islands of the West Indian archipelago 
with each other and with the mainland has been obtained already from the land fauna 
and flora of these islands.$ 
VY. Blind crayfishes have been found in the caves of Carniola and the United States. 
The Carniola blind crayfish is not merely specifically, but even generically, distinct from 
the other species of Europe, and belongs to the same genus as the crayfishes of the Atlantic 
slope of North America (Cambarus). As the genus Cambarus in North America was not 
developed under the influences affecting cavern life, it would seem that the generic iden- 
tity of the Carniola cave species with the North American forms cannot be due to simi- 
larity of surroundings, but rather to genetic connection. In other words, it is probable 
* Op. cit. 
+ Mem. Amer. Acad. Arts and Sci., New Series, VI. 377-452, 1857.— Proc. Amer. Assoc. Adv. Sei., 
21st Meeting, pp. 1-31, 1873. 
+ Histoire Naturelle des Crustacés, IIT. 584, 1840. 
§ Cf. Bland, Proc. Amer. Philosoph. Soc., XII. 56, 1871; Ann. Lye. Nat. Hist. N. Y., X. 311, 18745 
Ann. N. Y. Acad. Sci., II. 117, 1880. Eggers, Bull. U. S. Nat. Mus., No. 18, 1879. The extine¢ fauna of 
Cuba includes a giant sloth, Megalonyx (Leidy, Proc. Acad. Nat. Sci. Phila., 1868, p. 178); and in the little 
island of Anguilla, which is only thirty-five square miles in area, are found the fossil remains of several species 
of gigantic rodents and a deer (Cope, Proc. Amer. Philosoph. Soc., XT. 183, 1869; Ibid., XI. 608, 1870). 
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