128 Descriptions of Preparations. 



repeated in each of the intervening segments of the body's length. 

 The anterior sucker is perforated centrally by the mouthy and is 

 prolonged superiorly into an obtusely lanceolate lip consisting of 

 four rings. It is not separated by any constriction from the rings 

 immediately succeeding it, whilst the posterior sucker is very 

 markedly so separated, has the anus opening in the line of this 

 constriction, and differs consequently still further from the anterior 

 sucker in being imperforate and having an evenly circular un- 

 interrupted rim. Ten eyes are carried in pairs upon the three first 

 rings of the upper lip-like portion of the anterior suckers, and also 

 upon the fifth and eighth segments, the ten eyes as thus arranged 

 forming an ellipse. 



The male generative orifice from which the penis is sometimes in 

 this species, and very ordinarily in the common Horse-leech, 

 Aulostoma gtdo, protruded when the animal has been killed with 

 chloroform, is visible in the interval between the twenty-fourth 

 and twenty-fifth segments; and at an interval of five segments 

 posteriorly, the female generative orifice is seen in the interval 

 between the twenty-ninth and the thirtieth segments. 



A series of raised granular but minute tubercles may be observed 

 crossing the dorsal line in many segments, and representing in 

 miniature the warty exterior of Pontobdella. 



The external colouration of the Leech is very variable, and hence 

 the more or less strikingly regular development of black patches at 

 intervals of five ring-s in the rust-coloured line on the dorsal is of 

 the greater morphological importance. The amount of pigment 

 specks on the ventral sui-face is especially variable, and there does 

 not appear to be any regularity as to their distribution when 

 present. 



For an excellent monograph of Hirudo Iledicinalis, see Brandt and 

 Ratzeburg, Medizinische Zoologie, 1833, Bd. ii., pp. 230-397, 

 Taf. xxviii., xxix. A, xxix. B, xxx. See also Moquin Tandon, 

 Monographic de la Famille des Hirudinees, 1 846 ; Leuckart, 

 Die Menschlichen Parasiten, 1 863, pp. 634-739 ; Claus, Grund- 

 ziige der Zoologie, pp. 154-161; Gratiolet, Ann. Sci. Nat., 

 Ser. iv., tom. xvii., 1862, pp. 177-182, for the general out- 

 lines of the body. 



For certain organs of which as many as sixty may be found upon 



