IV LUMBRICUS 139 



imprisoned in a special chamber which becomes cut ofE from the main 

 cavity of the somite. This chamber is the seminal vesiele.i A seminal 

 vesicle is formed in each of the somites (X and XI) in which testes are 

 present (Fig. 67, s.v.l. and s.v.Il.). Each is hke a rectangular box 

 walled in by thin membrane, the anterior and posterior walls being simply 

 portions of septa. As the quantity of developing microgametes within 

 the vesicle increases in amount the walls of the vesicle bulge outwards 

 at their lateral angles forming large pouches, three on each side, which 

 pushing the septa in front of them project into the cavities of neighbouring 

 somites and in a dissection form the most conspicuous parts of the 

 vesicles. Of these lateral pouches the anterior vesicle forms two pairs 

 — one from each angle — while the posterior vesicle forms only a single 

 pair — which are however the largest — from its posterior angles. 



From the coelomic cavity the gametes find their way to the exterior 

 through the paired genital ducts. These are simplest in the case of the 

 female organs. The duct — oviduct (Fig. 67, od) — is in this case a short 

 somewhat trumpet-shaped tube opening by a wide funnel-like mouth 

 through the septum bounding somite XIII on its posterior side, and 

 passing outwards and tailwards to open to the exterior by a minute slit 

 on the ventral surface of somite XIV. The trumpet-shaped coelomic 

 funnel of the oviduct bulges backwards on its inner side into segment 

 XIV as a rounded pocket — the receptaculum ovorum — in which eggs 

 accumulate and remain for a time before passing to the exterior. 



The male gametes reach the exterior on each side by a slit-like opening 

 with tumid lips on the ventral surface of somite XV (Fig. 62, (?). The 

 genital duct can be traced forwards from this as a straight slender tube 

 ■ — the vas deferens (Fig. 67, v.d) — very inconspicuous except when filled 

 with spermatozoa — more or less embedded in the inner layers of the body- 

 wall. Into the anterior end of this there opens a vas eflerens, a slender 

 contorted tube which comes to it from the anterior seminal vesicle and, 

 one segment further back, a similar vas efferens comes from the posterior 

 vesicle. Each vas efferens communicates with the cavity of the vesicle 

 by a very wide ciliated funnel (Fig. 67, c.f), the wall of which is deeply 

 frilled, folded backwards and forwards, so as to break up the mouth of 

 the funnel into a system of very fine chinks. These chinks are so narrow 

 that the sperm-morulae and other stages in the development of the 

 microgametes are effectively prevented from passing out, whereas the 



^ This name has unfortunately come into practically universal use. The 

 earlier naturalists more correctly applied the name testis to the whole cavity 

 full of developing microgametes instead of restricting it to the small mass of 

 germ -cells still attached to the lining of the cavity. 



