Shell of the Sea-Urchin. 



572 PHYSICAL GEOGRAPHY. 



Near many a bank or fountain, lake or rill ; 

 Search where thou wilt, each differs in his kind, 

 In form, in figure, differs." 



In cursorily surveying the distinctive characters of the animal races, it is usual to follow 

 the series ascending from the lower to the higher organisations. 



The class of Zoophytes, or plant animals, may be regarded as forming the first link in 

 the chain of animal life. It includes several families whose members in general are 



aggregated in a common living mass, as the 

 buds of a dicotyledonous tree are united 

 to the stems. This is the case with the 

 tribes of polypi, which have their special 

 habitation in the equatorial seas, and there 

 construct the coral reefs and islands. In 

 the Infusoria, or animalcula, chiefly found 

 in stagnant fresh water filled with vegeta 

 ble matter, and in common sea-water, a 

 real individual existence is developed, but 

 so exceedingly minute as to be seldom 

 capable of being traced except with the 

 aid of a microscope. The brown -coloured 

 fine dust, so often noticed in the Atlantic, 

 which has fallen in such quantities upon 

 vessels as to soil every thing on board, and even cause them to run ashore through 

 the obscurity of the atmosphere, consists principally of Infusoria. Some of the species 

 multiply at a prodigious rate ; for Ehrenberg calculated that, in twenty days, a single 

 individual may increase to a million. In the class of Mollusca, whether naked or 

 testaceous, that is, furnished with a shelly covering more or less thick and entire as in 

 the case of the oyster, lobster, and crab a well-defined individual existence appears. 

 This order is very extensively diffused ; but several species are exclusively confined to 

 particular seas, the pearl-oyster only arriving at perfection in the equatorial ocean. The 

 Indian and the Mediterranean seas are the chosen haunts of the Pinna marina, whose 

 filaments rival in appearance the most glossy silks. Different kinds of shells are found 

 on the shores of South America and Australasia ; also in each of these districts with a 

 change of latitude ; and the tropical forms are distinct from those of extra-tropical situ 

 ations. The natural distribution has, however, been interfered with by accidental causes ; 

 for many molluscoj, adhering to the bottoms of ships, have been transported to foreign 

 parts of the ocean, which have become peopled with new species. Thus the shelly ship- 

 worm, Teredo navalis, so peculiarly destructive to vessels, boring with ease and rapidity 

 into the stoutest oak planks, has in this way been conveyed to the waters of Australia. 

 Some unknown cause brought grea.t numbers in the years 1731 and 1732 to the banks of 

 Zealand, and excited the fears of the Dutch for their piles ; but they departed without 

 doing much mischief, probably to seek a warmer temperature. 



A further advance in ascending the scale of animal existence brings us to the Insect 

 tribes, some of which are extensively disseminated ; as gnats, bees, and flies. The thistle- 

 butterfly, la belle dame, is common in Sweden, throughout midland and southern Europe, 

 and found also at the Cape of Good Hope. Others, as Prichard observes, are especially 

 limited in the sphere of their existence by the presence of particular plants, which afford 

 them habitation and sustenance ; and in general, where countries are separated by great 

 distances, though their temperature and soil are the same, the insects inhabiting them are 



