266 



THE INVERTEBRATA 



testes discharge into a common vas deferens on each side; the two 

 vasa unite anteriorly to form a median penis. Similarly the two 

 oviducts join and the eggs pass through a single albumen gland and 

 vagina to the exterior. The spermatozoa, united in bundles, are 



ect. 



n.c. 



Fig. 196. Transverse sections of Hirudinea to show the progressive restriction 

 of the coelom. A, Acanthohdella, B, Clepsine, C, Hirudo. In A the coelom 

 {coe.) is continuous but encroached upon by growth of parenchyma (stippled). 

 In B it is broken up into a system of sinuses, d.s. dorsal; v.s. ventral; h.s. 

 hypodermal sinus; l.s. lateral and i.s. a network of intermediate sinuses. In 

 C the sinuses (outlined in black) are reduced in size, and there is no inter- 

 mediate network, n.s. the nephrostomial sinuses, branches of the ventral sinus, 

 contain the testes (i); botryoidal tissue {b.t.) is present; ch. chaetae; cm» 

 coecum ; cr. crop ; d.v. dorsal, l.v. lateral, v.v. ventral blood vessel ; gl. glands ; 

 m.c. circular, m.l. longitudinal muscles; ect. ectoderm; nep. nephridium; 

 oe. oesophagus; n.c. nerve cord; per. peritoneum; s.o. sense organs. 



deposited on the body of another leech and appear to make their 

 way through the skin to the ovaries where fertilization occurs. The 

 eggs are laid in cocoons, the case of which is formed by clitellar 

 glands in the same way as in Lumbricus. 



