ii6 ANNELIDA OR ANNUL AT A 



Digestive System. — The digestive tract consists of the mouth, 

 with three jaws, armed with chitinous teeth, a pharynx, esophagus, 

 crop with eleven lateral diverticula, stomach and an anus. A 

 secretion called deutero-albumose (hirudin) prevents the blood from 

 clotting. It is formed by the glands located near the jaws. The 

 muscular pharynx dilates to receive the blood and passes it on 

 through the short esophagus to the crop which has 1 1 pairs of lateral 

 diverticula and which stores the blood until it is digested in the 

 globular stomach. No digestion takes place in the lateral " pockets." 

 The rectum., situated between the last two diverticula^ is separated 

 by a sphincter muscle from the true stomach. It ends as the dorsal 

 anus near the posterior sucker. 



Circulatory System. — There are two main lateral vessels running 

 longitudinally. These are connected with each other by looped 

 vessels which give off many branches. There are two sinuses., one 

 dorsal and one ventral, with numerous primitive lymphatic vessels. 

 The blood is red with many white blood corpuscles. The leech has 

 a body temperature of about 57° F., except when it has just gorged 

 with mammalian blood. 



Respiration is carried on by the highly vascular skin. Experi- 

 ments have shown that leeches will live in pure Nitrogen for from 2 

 to 6 days. 



Excretory System. — Seventeen pairs of nephridia, from the second 

 to the eighteenth segment, open laterally on the ventral surface. 

 There are about five external annulations to each true segment. 



Reproductive System. — Leeches are hermaphroditic. There are 

 nine pairs of diffuse testes^ which are situated on each side of the 

 nerve cord. The spermatozoa pass by a short canal into the long 

 wavy vasa deferentia. From these they travel in the epididymis 

 where they are bundled into spermatophores and pass out by the 

 penis. They leave the body in the mid-ventral line between rings 

 30 and 31. 



Two small tubular ovaries are enclosed in vesicles., continuing into 

 oviducts which unite as a uterus. Glandular cells secrete into the 

 uterus a mucus fluid which later hardens into a cocoon. 



The genital pore is situated in the mid-ventral line at rings '^^ 

 and "^^^d (segment 11). Conjugation consists in the actual simul- 

 taneous insemination of each worm by the other. Spermatophores 

 may remain for a long time in the uterus or may travel almost 

 immediately in the female ducts and fertilize the eggs at the ovaries. 

 Cocoon formation results. 



