ORDER ANNULATA APODA. 107 



parts of the surface of the body, for which use it is emi- 

 nently adapted. 



There are as many as twelve or fifteen species of these 

 creatures, but only two have been employed in medicine, 

 namely, the Hirudo mediciiialis, which may be known 

 by having six yellowish lines, or striae, on its back, 

 while the under-part is of a grayish hue spotted with 

 black, but, as we shall presently see, these markings 

 are not uniformly found ; and the Hirudo troctina, of a 

 brownish colour, the upper part of the body marked with 

 black spots, each of which is surrounded with a golden- 

 coloured ring, the sides of a dingy yellow, and the under- 

 part of a yellow^ish green with black spots. 



The first of these species, the medicinal leech, is 

 common throughout the whole of Europe, but is much 

 more abundant in the Southern parts ; it is generally 

 about three inches in length. Formerly it was very 

 abundant in Great Britain, but the improvements in 

 agriculture, and the consequent drainage of the land, 

 together with the great use made of it in medicine, have 

 of late years rendered it of less frequent occurrence. On 

 this account great quantities of leeches are imported; 

 these chiefly come from Bourdeaux and Lisbon. On a 

 moderate calculation, it appears that, in England, on an 

 average, out of every hundred leeches employed, ninety- 

 nine maybe considered of foreign production; these dif- 

 fer from the English leech in being somewhat larger, and 

 having the under-part of a uniform colour, without spots. 

 Some idea may be formed of the number of leeches 

 iised in medicine by the statement, that in the hos- 

 pitals of Paris alone, 300,000 were employed in one 

 year. The prevailing colour of the medicinal leech 

 appears to vary according to the nature of the soil on 



H 2 



