HIRUDO MEDICINALIS 



l8l 



in the midst of the anterior sucker, and the anus is a minute 

 opening above the base of the hinder sucker. The male and female 

 genital openings are median on the second annuh of the loth and 

 nth segments respectively. On the last annulus of each segment 

 from the sixth to the twenty-second, are the openings of a pair 

 of nephridia. On the first annulus of each segment is a transverse 

 row of minute sense-papillae. On the head a pair of these in each 

 segment are transformed into minute eyes, recognisable by their 



Fig. 129. — A transverse section of the medicinal leech. — After Bourne. 



b.t., Botryoidal tissue ; cm., circular muscles ; cap., capillary ; cr., crop ; cr'., a caecum of the same ; cu ; 

 cuticle ; d.m., dorsoventral muscle ; d.s., dorsal sinus ; ep., epidermis ; g.c, gland cells ; l.m., longitudinal 

 muscles ; l.v., lateral vessel ; n.c, nerve cord ; t., testis ; t.s., testis sinus, with end of nephridium., 

 v.d., vas deferens ; v.s., ventral sinus. 



pigment as dark spots. There are no chaetae. The worm can walk 

 by looping Hke a ' looper ' caterpillar, and swim by undulation 



of its body. 



The body is covered by a thin cuticle (Fig. 129), which is shed 

 from time to time. Under this Hes an epidermis, between the bases 

 of whose cells run blood capillaries, so that the skin is a respiratory 

 organ, in which the blood is exposed to the surrounding water. 

 Below are circular and longitudinal muscle-layers, and within 

 these a layer of botryoidal tissue, composed of branched canals, 

 whose walls are laden with black pigment, while their cavity is 

 full of blood. This tissue takes the place of a perivisceral cavity 

 and embeds the gut. The mouth is provided with three jaws, 

 which are compressed cushions of muscle covered with a finely 



