ANNELIDA : THE LEECH 



237 



than the rest and extends backwards on each side of the 

 remainder of the alimentary canal. This consists of the 

 stomach — a narrow tube, with an enlargement at its start 

 and a spiral fold of its inner wall — the intestine, narrower 

 than the stomach, and the rectum, somewhat wider. The 

 blood sucked for food is stored in the crop, whose caeca 

 are more or less dilated according to the amount of 

 their contents, and passed drop by drop into the stomach, 



d - S - b.t 



Fig. 152. — A transverse section of the medicinal leech. — After Bourne. 



b.t., Botryoidal tissue; cm., circular muscles; cap., capillary; cr., crop; ci* '., a 

 csecum of the same; CM., cuticle; dm., dorsoventral muscle; d.s., dorsal 

 sinus ; ej>., epidermis ; g.c, gland cells ; /. «., longitudinal muscles ; Lv., lateral 

 vessel ; n.c. t nerve cord ; t. t testis ; t.s., testis sinuSj with end of nephridium ; 

 v.d., vas deferens. 



where it at once turns green and then is digested. A 

 full meal will last the animal for several months or a 

 year. Seventeen pairs of nephridia lie in segments 7-23. 

 Each is a mass of glandular tissue traversed by a system of 

 intracellular ductules. There is no internal opening, but 

 those which lie in the testis segments have a swollen end 

 lying in the capsule of the testis, and bearing a number 

 of ciliated funnels which do not communicate with the 

 ductules. There are two systems of tubes which contain 

 a fluid like blood — a red plasma with a few colourless 



