Reproductive Organs^ &c. of Arenicola, 297 



and Cosraovici's drawing shows it very well. They extend 

 obliquely across the neck and end just above the posterior 

 dilated part of the nephridium. From these blood-vessels 

 pass into the tissue of the nephridium in all directions and 

 posteriorly into the upper part of the gonad, which lies at the 

 lower end of the neck. 



The tliin strips of muscles which stretch across the 

 nephridium and bind it down to the side of the body have a 

 slight attachment to these processes, but not to the nephri- 

 dium ; hence the neck of the nephridium can be moved 

 about, and may be found lying parallel to the longitudinal 

 axis of the body (PI. XIII. fig. 1), or bent outwards so that 

 it is almost at right angles to this axis, the nephrostome 

 being then in a transverse plane (fig. 2). This movement 

 is in all probability executed by means of the transverse 

 strips of muscle through the connexion mentioned above. 



The particular structure of the nephridium need not be 

 more than mentioned, as Benham has fully described it, and 

 the sections agree with his descriptions. The posterior dilated 

 part, however, seems to be wholly glandular, without any 

 muscular fibres. Such fibres appear as the dilated portion 

 narrows between the longitudinal strands of muscle along the 

 body-wall. To these strands the nephridium is in no way 

 attached, and such points to the conclusion that the nephridium 

 and the circular muscles are developed sooner than the longi- 

 tudinal ones ; and this finds further confirmation in that the 

 nephridia and circular muscles, as Benham mentions, are 

 present in the post-larval stages, whilst the longitudinal are 

 hardly, if at all, evident. 



Where the nephridium becomes connected with the trans- 

 verse muscles muscular fibres are plentiful in its walls. 



The canal to the exterior runs for a short distance round 

 the body within the circular muscle-band, so that the external 

 opening is controlled both by the muscles of the body-wall 

 and by the muscular fibres of the nephridial wall. These 

 latter are in reality but continuations of the circular fibres of 

 the body-wall. 



The nephridium of those with ripe products differs slightly 

 from the normal, being more elongated and the walls thinner 

 and more attenuated. 



The reproductive organs (PI. XV. fig. 5) can be found with- 

 out much difficulty by means of sections of the nephridia — 

 the second, third, and fourth pairs especially — of those animals 

 which contain the genital products. Cunningham narrates that 

 " loose cellular masses were often seen in the neighbourhood 

 of the nephridia," and that " these were traced to the cord of 



