RANGE OF THE CRUSTACEANS 183 



the lobster, and at last it appears in the compact shape which 

 constitutes the highest perfection of crustacean life. 



Providence has ordained that each class of animals should not 

 only branch out into a multiplicity of forms, so as to be able to 

 adapt itself to an immense diversity of local circumstances, but 

 also that it should spread itself as far as possible over the surface 

 of the globe. 



Thus, though the crustaceans have their chief seat in the 

 ocean and its littoral zone, yet several of their species ascend 

 into the regions of eternal snow, while others hide themselves in 

 the perpetual darkness of subterranean grottoes. The famous 

 cave of Adelsberg in Carinthia is tenanted by several crustaceans, 

 and the alpine-flea is found on the Aar-glacier, 8,500 feet above 

 the level of the ocean. 



Many crustaceans, averse to the briny sea, delight in the 

 sweet waters of the river or the lake ; others, finding not even 

 sea-water salt enough to their taste, can only enjoy existence in 

 saline springs ; while others again entirely abandon the liquid 

 element and live on the dry land, either sojourning, like our 

 wood-lice, under stones and in cellars, or, like the land-crabs of 

 the West Indies, in shady forests, where though they breathe, like 

 their aquatic relations, through the medium of gills, the peculiar 

 construction of their respiratory organs and the perpetual mois- 

 ture of the climate render their existence possible. 



While myriads of crabs people the slimy lagunes, or burrow 

 in the sands skirting the ocean, or seek a shelter among the 

 fronds of submarine forests, others love to sojourn in the deeper 

 waters, or even to perform long sea-voyages, like the Nautilo- 

 grapsus, which, though ill-formed for swimming, finds means 

 to satisfy its roving propensities by clinging to the back of a 

 turtle. 



While the lower crustaceans abound in the Polar seas, crabs 

 are completely wanting in those gelid waters : their number 

 increases on advancing towards the equator, and attains its 

 maximum in the torrid zone. Here we find the most remark- 

 able and various forms ; here they attain a size unknown in our 

 seas ; and here they do not, as with us, inhabit the salt waters 

 only, but also people the brooks and rivers, or even constantly 

 sojourn on land. 



With the exception of the terrestrial Onisci, which chiefly 



