X] LUMBRICUS 155 



of the hand being attached and the fingers free. Their ducts which 

 convey away the spermatozoa are called the vasa efferentia. 

 They have similar funnel-shaped openings to those of the oviducts 

 and they traverse the septum behind the segment in which these 

 openings lie, but they do not at once open to the exterior. The 

 two ducts of each side unite in the twelfth segment, and the com- 

 mon duct thus formed runs back to open by a pore with swollen 

 lips on the fifteenth segment, i.e. the one behind that on which the 

 oviducts open (7, Fig. 64). It is termed the vas defer ens. 



Since both genital ducts and nephridia are tubes opening at the 

 inner end into the coelom and at the other end to the exterior, it 

 used to be supposed that they were the same kind of thing, in a 

 word that the genital ducts were modified nephridia. The study 

 of their development has proved that such is not the case. The 

 genital duct arises as an outgrowth of the coelomic sac it is 

 therefore termed a coelomiduct. The nephridium is always an 

 ingrowth from the ectoderm. The so-called nephridia of Mollusca 

 are really modified coelomiducts, and are not comparable with the 

 nephridia of Annelida. The ovaries of the earthworm lie freely in 

 the body-cavity and can be seen readily if the intestine be removed, 

 each pair of testes and the corresponding inner funnel-shaped 

 openings of the vasa deferentia are concealed by a certain sac or 

 bag called the vesicula seminalis, and it is only by cutting 

 away the wall of this sac that these structures come into view 

 (4, Fig. 64). Each vesicula seminalis is a flat, oblong bag ex- 

 tending backwards from the front wall of the segment in which it 

 lies and situated beneath the alimentary canal. The angles of the 

 front vesicula seminalis are produced into two long pouches which 

 project upwards at the sides of the alimentary canal, and are often 

 called lateral vesiculae semiuales, though they ought to be termed 

 lateral horns of the anterior vesicula seminalis. Similar projections 

 are produced from the hinder angles of both of the anterior 

 and of the posterior vesiculae seminales, so that on opening a worm 

 three pairs of grayish white sacs are seen at the sides of the gut. 

 The study of the way in which the vesicula seminalis is formed 

 shows that the space it contains is really part of the coelom which 

 has become cut off from the rest by the outgrowth of folds from the 

 septa, so that, although at first sight the testes seem to differ from 

 the ovaries and to be exceptions to the general rule that repro- 

 ductive cells have their origin from the walls of the coelomic 

 cavity, a closer examination shows that this apparent divergence 

 is not a true one. 



