98 ZOOLOGY. 



much overrated. They have been made to fast two or three years ; they 

 require five years to become large enough for use, and they may live twenty 

 years. They seem not to multiply rapidly when they have not access to 

 blood ; and on this account, cows and horses are driven into the breeding 

 ponds, and so frequently, that they become emaciated from the loss of 

 blood. Three millions of leeches are used annually in Paris ; and four 

 dealers in London import upwards of seven millions annually. In 1819, 

 five or six millions were used in Paris, at a cost of 120,000 francs ; and in 

 1827, thirty-three millions were required in France. To preserve them in 

 health, they must have clay, sticks, &c., to crawl amongst, to assist them in 

 casting the skin, this part being often renewed ; and if the old surface is not 

 removed, respiration is interfered with. 



Gervais, who insists upon the identity of the Annelida and Entozoa, places 

 the family which includes Sipunculus (p. 42) next to the Hirudinidse. 



Fam. 2. Lumhricidm. The genus Lumhricus {pi. 77, figs. 38, 44) 

 contains the earth-worms, known by their habits of living in the earth, and 

 coming to the surface in wet weather and at night. The body is reddish 

 or bluish, cylindrical, composed of many rings, the head indistinct, the 

 mouth without teeth, and having neither eyes nor tentacles. The segments 

 are provided beneath with minute bristles, and above with one or two 

 pores. At certain periods, in some of the species, the part of the body con- 

 taining the reproductive organs has a broad collar named the clitellum. 



These worms are monoicous, they feed upon the organic matter contained 

 ,in the soil, generally ejecting the indigestible portion at the surface of 

 the ground. Some species live in the soft mud at the bottom of streams, 

 and the ordinary species may be kept in vessels of mud and water. The 

 largest European species is a foot and a half long, but there are several 

 exotic species several feet in length. 



Earth-worms are very useful to the soil, as their perforations open it and 

 allow the air and moisture to penetrate. They also assist in ameliorating 

 it, and in increasing its depth ; and where they are abundant, it is probable 

 that every inch of soil has passed through their digestive system. In old 

 unploughed pastures the soil formed by their castings is known to have 

 amounted to an inch in depth in five years. 



Nais {pi. 77, figs. 9, 10), which belongs to this family, has the segments 

 with lateral spines or fascicles. The old genus thus named by Müller, has 

 been subdivided by more recent writers. They inhabit the fresh waters. 



T'uhifex is a genus of microscopic worms found in fresh water, where 

 they form a tube in the mud, whence they project the greater part of the 

 body, waving it about, but instantly withdrawing when disturbed. Several 

 species of the United States have been described. 



Fam. 3. Echiwri. These have been alluded to in page 42. The body 

 is short, composed of but few indistinct articulations, cylindrical, sacciform, 

 provided with pairs of retractile bristles upon some of the segments. 

 Thala-ssema echiurus^ of the European seas, is the best known species. 



Fam. 4. Maldam^im. This is one of the families of the distinguished 

 naturalist Savigny, who accompanied the French expedition to Egypt. In 

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