ZOOLOGY. 339 



cats, seahogs, vultures, crocodiles, vipers, and rattlesnakes buried in 

 the soil, and that the gaseous emanations which are the vehicles of 

 this aroma are only disengaged when the earth containing these 

 bodies is saturated with water. This explanation seems problemati- 

 cal, and analogous to the ancient hypothesis which attributed the 

 phosphorescence of the sea to cadaveric debris, while it is produced 

 by a multitude of living beings of different species. Possibly these 

 musky emanations of tropical soils are due to the development of in- 

 ferior organized beings, probably cryptogamic in character. Cosmos. 



THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 



Mr. Darwin, in his recent work on the " Origin of Species," ener- 

 getically denies the doctrine of the origination of organic forms from 

 " specific centres." Wherever the same species are found in distant 

 districts the fact may, he thinks, be most probably accounted for by 

 migration. On this view the supreme importance to geographical 

 distribution of the presence of impassable barriers is readily under- 

 stood ; the seas on either side of a continent, and the continents on 

 either side of a deep and wide ocean, being respectively inhabited by 

 very different races. In taking this view, however, he does not make 

 so much use as some naturalists the late Edward Forbes, for in- 

 stance have done of the influence of geological changes in uniting 

 districts which are now separated, but is inclined to rely more exclu- 

 sively upon the ordinary and still existing means of dispersal. These 

 are, he thinks, both more numerous and more effective than are gen- 

 erally supposed. He shows that the seeds of many plants can bear 

 long immersion in sea-water, or imprisonment in the crops of birds, 

 without losing their vitality; and they may also be transported 

 largely from place to place in the mud adhering to the feet of living 

 birds. Of the cases which are generally cited as militating against 

 the doctrine of a single centre of creation, the two strongest are per- 

 haps the presence on distant mountains of the same species, and the 

 wide distribution of fresh-water forms. The former fact Mr. Darwdn 

 accounts for by the uniform southward migration of northern forms 

 during the cold period which preceded and accompanied the glacial 

 epoch ; some of which forms, when the temperature of the region 

 again rose, instead of returning northward, retreated into the moun- 

 tains of the district in which they chanced to be. The wide distri- 

 bution of fresh-water species he attributes to slight geological changes 

 of level, which have at more or less remote periods enabled rivers, 

 which now are without inter-communication, to flow into each other ; 

 and also, in no small degree, to the agency of living birds already 

 alluded to. The following passage, bearing on this latter point, is so 

 interesting, that we give it in Mr. Darwin's own words : 



" I have before mentioned that earth occasionally, though rarely, 

 adheres in some quantity to the feet and beaks of birds. Wading 

 birds, which frequent the muddy edges of ponds, if suddenly flushed, 

 would be the most likely to have muddy feet. Birds of this order I 

 can show are the greatest wanderers, and are occasionally found on 

 the most remote and barren islands in the open ocean ; they would 

 not be likely to alight on the surface of the sea, so that the dirt 



