76 THE BIOLOGY OF AN ANIMAL. 



ovorum, the ova taken up by tlie funnel are temporarily stored 

 before passing out to the exterior. 



It is probable that the eggs never float freely in the coelom, 

 but drop out of the ovary at maturity directly into the mouth of 

 the funnel. They pass thence into the receptaculum, where they 

 may remain for a considerable period. 



The sperm-ducts (vasa deferential) (sd, Fig. 29) are very 

 long slender tubes, open like the oviducts at both ends. The 

 outer opening is a conspicuous slit surrounded by fleshy lips 

 (Fig. 21), on the ventral side of the 15th somite. From this 

 point the duct runs straight forwards to the 12th somite, where 

 it branches like a Y, the two branches passing forwards to ter- 

 minate, one in the llth somite, the other in the 10th. Near its 

 end each branch is twisted into a peculiar knot and finally ter- 

 minates in an immense ciliated funnel (the so-called "ciliated 

 rosette"), the borders of which are folded in so complicated a 

 manner that they form a labyrinthine body, the true nature of 

 which can only be made out in microscopic sections. 



The two pairs of sperm-funnels (Fig. 29) lie in the 10th 

 and llth somites, immediately posterior to the respective testes, 

 i.e., they have essentially the same relation to the testes as that 

 of the oviduct-funnels to the ovaries. 



The testes and sperm-funnels can be readily made out only in young 

 specimens. In mature worms they are completely enveloped by the semi- 

 nal vesicles described below. 



Seminal vesicles. These, the most conspicuous part of the 

 reproductive apparatus, are voluminous pouches in which the 

 sperm-cells undergo their later development, after leaving the 

 testis. They are large white bodies lying in somites 9 to 12 and 

 usually overlapping the oesophagus in that region. In all cases 

 there are three pairs of lateral seminal vesicles, viz., an anterior 

 pair in somite 9, a middle pair in somite 11, and a posterior pair 

 in somite 12. In immature specimens these six are entirely 

 separate, and allow the testes to be easily seen. In mature 

 worms (as shown in Fig. 29) the posterior pair of lateral 

 vesicles grow together in the middle line, thus forming a pos- 

 terior median vesicle lying below the alimentary canal in the 

 llth somite. In like manner an anterior median vesicle is 

 formed in the 10th somite by the union of the two anterior pairs 



