298 SCIENCE OF AGRICULTURE. Pakt II. 



degree in those of the south of England and the north of Scotland. Similar appearances 

 present themselves among the sheep of warm and cold countries : the fleece of those of 

 England consists entirely of wool, while the sheep of Shetland and Iceland possess a 

 fleece, containing, besides the wool, a number of long hairs, which give it an appearance 

 of being very coarse. 



2005. The particular or local distribution of animals is affected by various causes which 

 have little influence on their geographic distribution. Thus the purely insectivorous 

 birds of the family Sylviadte feed on all kinds of small insects, without regard to any 

 particular species; yet the Sylviadae of America and those of Europe are each 

 characterised by a peculiarity of structure which invariably designates the continent to 

 which they belong. The wryneck is represented in America by the Oxyrhynchus cris- 

 tatus Swains. {Zoo/. III. i. p. 149.) ; yet neither of these birds are found to inhabit all 

 parts of their respective continents : their range, on the contrary, is regulated by tem- 

 perature, food, and other circumstances connected with local distribution. (Swainsoii's 

 MSS.) 



2006. From temperature originate all the causes which affect local distiibution, namely, 

 food, situation, and migration. Were the climate of this country as unchanging as that 

 of Brazil, the insects which now have only a single brood in the year might then produce 

 several, and the swallow would no longer be obliged to quit us as now, for food in other 

 climates, as soon as our insect season was at an end. Migration and torpidity are 

 equally the effect of temperature ; the first depends upon the effect which the changes of 

 the seasons produce in the abundance or scarcity of food, whether animal or vegetable ; 

 the latter is a state of inaction during which the necessity for daily nourishment is 

 suspended. 



2007. The miration of birds and offsh is more extensive than that of quadrupeds. 

 The birds of the Polar regions migrate to Britain during severe winters ; while those of 

 Africa come to us, in that season when the southern heats are most intense ; but the same 

 species which is migratory in one country is in some cases stationary in another. It is 

 stated that the linnet is migratory in Greenland, but that it is stationary in Britain. 



2008. The torpidity or hybernation of animals is evidently designed to suspend the 

 necessity of taking food during the winter ; althaugh in some cases a small stock of 

 provisions is laid up, most probably to serve for nourishment previously to entire torpidity 

 taking place. Several quadrupeds are subject to this partial suspension of life, as the 

 do'rmouse, hedgehog, bat, marmot, &c. It is said that birds have sometimes been found 

 in a similar state ; but this is very questionable. Among insects, on the contrary, 

 torpidity is very common, and a large proportion, when undergoing transformation, pass 

 a considerable part of their lives in this state. 



2009. Situation has an extensive infvence on the local distribution of animals, although 

 it has little on the geographical distribution of groups. Air, earth, and water have their 

 distinct inhabitants, ich are again restricted to certain situations in their respective 

 elements. The higher regions of the air are frequented by the eagle and falcon tribes ; 

 the middle by the air-feeding birds ; and the lower by insects which merely jump, or just 

 fly above the ground. The different situations on land, as mountains, plains, woods, 

 marshes, and even sandy deserts, are each peopled by distinct races of beings, whose 

 subsistence is sought for and furnished in peculiar spots. Thus the range of any par- 

 ticular species is seldom or never continuous, or uninterrupted to its confines ; but is 

 rather dependent upon local causes, quite unconnected with geographic division. Water 

 is either the total o)c the partial residence of animals innumerable ; but here situation has 

 an equal influence ; the deeps and the shallows of the ocean, its exposed or sheltered 

 shores, its sandy, rocky, or muddy bottoms, are each the resort of different beings, 

 widely distinct from those residing in the streams, lakes, rivers, and estuaries of fresh 

 waters. It is principally among insects that we find the perfect animal inhabiting a 

 situation different from that which was essential to its existence in an imperfect state. 

 The larvae of the May-fly, known to the vulgar by the name of case-woiTn (Trichopterte 

 Kirby), and of all the Libellula2 live entirely in the water, preying upon other aquatic 

 insects ; but as soon as the period of transformation arrives, they crawl on the 

 plants, just above the surface, and bursting the skin, become winged insects, which im- 

 mediately commence an uninterrupted war upon others in their new element. The larva 

 of the well known ^ph(5mera is likewise aquatic, and spends nearly all its life in water ; 

 but the perfect insect is without jaws, mounts into the air, and seems born but to flutter 

 and die. Many of the Coleoptera pass the first period of their existence entirely un- 

 derground, others in the trunks of trees ; and others again in putrid substances ; 

 situations very different from those which they frequent when arrived at maturity. 

 Lepidopterous insects, after emerging from the eggs, undergo three changes, all of which 

 are in situations totally opposite. In the larva state they reach their full dimensions 

 by feeding upon the leaves of vegetables ; they^next pass into pupa?, and become torpid 



