70 



THE MEDICINAI> LEECH 



the nerve cord and unites with the left one to form a common median duct. 

 This common duct is surrounded by the albumen gland, and it opens into a 

 curved muscular tube, the vagina, which opens in the middle line on the ventral 

 surface of the second annulus of the 11th segment. 



The testes are nine pairs of spherical sacs lying along each side of the ventral 

 sinus in segments 12-20. Each gives off from its outer surface a narrow efferent 

 duct, which joins the larger vas deferens running parallel to the alimentary canal. 

 In the 10th segment each vas deferens increases in width and forms a complex 

 coil, the epididymis or vesicula seminalis, giving rise anteriorly to a widened 

 muscular tube, the ductus ejaculatorius. From each ductus ejaculatorius a 

 narrow duct passes to the penis, which is a curved muscular organ protrusible 

 through the male genital aperture in the middle Une on the ventral surface of 

 the second annulus of the 10th segment. 



Make a drawing to show the Nervous System and the Reproductive System. 



nsi n.s i 



Fig, 23. — Transverse Section (diagrammatic) through the middle of the body of the 

 Leech (Hirudo). A nephridium is shown (entire) on the left side of the figure. 

 After Marshall and Hurst. With permission from Parker and Haswell's Text-book 

 of Zoology. 



cit. cuticle ; tJ.cjj. epidermis ; cm. circular and oblique muscles ; l,m. longitudinal muscles ; d.ii.m. dorso- 

 ventral muscles ; h,t. botryoidal tissue ; cr. crop ; or', diverticula of crop (storing pockets) ; d.s. dorsal 

 sinus; Lv. lateral sinus or "blood-vessel"; v.b. ventral sinus; n.c. nerve cord; n,s. uephrostomial 

 sinus ; to. testis ; v.d. vas deferens ; wpli. section of nephridium ; nipli. 1. anterior limb of main lobe of 

 nephridium ; nph. ^. posterior limb of main lobe of nephridium ; nph. 3. apical lobe of nephridium ; 

 nph. k. testis-lobe of nephridium ; nst. * ' cauliflower lobe " or inner end of the testis-lobe (nephrostome) ; 

 vs. vesicle or bladder of nephridium ; Tip. external apei-ture of nephridium or nephridiopore. 



Transverse Section of Body. 



In a transverse section of the body of a Leech the following structures may 

 be seen : — 



(a) The thin cuticle. 

 (6) The epidermis. 



