Benham. — Oligochaeta from Kermadec Islands. 



181 



cells, which constitute a diffuse " prostate," as in other species of the genus. 



When it enters segment xi it lies low down, close to the nerve-cord; but 



it gradually passes outwards and up. 

 wards to lie at the side of the oeso- 

 phagus at about the middle of the 

 segment. It continues to rise till at 

 the hinder end it is on the level of 

 the roof of the oesophagus, or even 

 higher. At this point the prostate 

 cells cease, the sperm-duct bends 

 abruptly downwards, and passes some- 

 what forwards and outwards to open 

 into a suddenly enlarged terminal 

 " atrium," or " penial sac " as 

 Moore (13) calls it.* The atrium, in 

 its turn, communicates with the 

 posterior extremity of the invagi- 

 nated body - wall, which encloses a 

 chamber to which Goodrich has 

 given the name " spermiducal cham- 

 ber." a median structure which opens 

 by a longitudinal slit-like aperture to 

 the exterior. 



The sperm-duct, from funnel to 

 its opening into the atrium, is lined 

 with ciliated epithelium, outside which 

 is a laver of circular muscles, as 

 Goodrich has figured. At its entrance 

 into the atrium the duct traverses a 

 group of large (? gland) cells which 

 project into the wide lumen of the 

 atrium, the wall of which is muscular. 

 The anatomical relations suggest that 

 this region is eversible, or is a part of 

 the " chamber " : the muscular duct 

 would then act as a " ductus ejacu- 

 latorius." 



In some species of the genus this 

 region has rather tall gland-cells form- 

 ing the epithelium, but in the present 

 case the cells are low, and not ap- 

 parently glandular. However, it may 

 be that in certain phases of sexual 

 maturity they do become higher, and 

 take on a definitely glandular structure. 

 The " spermiducal chamber " (or 

 "atrium" as Moore, unfortunately, 

 calls it) is a hemispherical sac pro- 

 jecting into the cavity of the segment, 

 occupying nearly half its extent. It 

 is, as Goodrich (8) has shown, merely 



* it seems to me that^thisjregion corresponds to what is usually called " atrium " 

 in the other Tubificids ; the term " penial sac " is used in another sense. 



