854 PROP. G. C. BOURNE ON THE [ISTov. 17,- 



before. The nerves c^j). pass under the pleural ganglia and take- 

 then- origin from the swollen anterior ends of the pedal cords.. 

 They are slightly asymmetrical, but are distributed on both sides, 

 of the body to the opercular lobe. 



As I have already pointed out, authors differ in their identi- 

 fication of the subintestinal ganglion. The conical enlargement 

 of the origin of the subintestinal nerve — it has in all species the- 

 shape represented in fig. 36, and is not a rounded ganglion as 

 figured by Bouvier — was identified by de Lacaze-Duthiers as- 

 the subintestinal ganglion ; and Bouvier and Lenssen have 

 accepted this view. Boutan and Haller, on the conti^ary, claim 

 that the subintestinal is represented by an elongated ganglionic- 

 swelling on the right of the visceral commissure just where the 

 latter turns towards the left to run through the large blood-sinus- 

 leading in the direction of the uropore. Concerning this gangliort 

 I have something to say. As is shown in the accompanying text- 

 figure (172), it is an elongated and rather diffuse ganglion from 

 which three main nerves are given off. The most anterior (n^) 

 passes inwards, forwards, and ventralwards and supplies (as far 

 as I am able to determine) the coils of the intestine lying 

 below and to the side of the anterior part of the radular sac. 

 Lenssen has described a similar nerve in N.fltiviatilis, but in 

 this species it is given off some distance in front of the ganglioUy 

 and, curiously enough, he says that some of its branches are 

 distributed to the stomach ; as a matter of fact, they pass in an 

 opposite direction. The second nerve (?r) is rather stout and' 

 passes outwards into the tissue overlying the posterior part of 

 the right columellar muscle. It does not penetrate the muscle, 

 but turns sharply backwards, and I was able to trace it in sections 

 as far as the pedicle of the visceral mass, and thence alongside 

 the oviduct to the ovarian follicles. Lenssen has described a 

 similar nerve in JV.Jluviatilis arising like the first well in front of 

 the ganglion ; this he calls a columellar nerve, but I am of the 

 opinion that it has the same distribution as that just described, 

 though I could not follow it very well in my sections. The- 

 third nerve has been quite incorrectly described by previous 

 authors. As shown in the text-figure, it is very short and stout, 

 and passing downwards enters at right angles a stout and' 

 relatively long nei-vous cord (g.g.), which is thickly coated with 

 nerve ganglion- cells. This cord may properly be described as a 

 genital ganglion. It is closely attached to the gonaduct, and its 

 lower end (gn^) turns sharply backward and passes to the spermato- 

 phore-sac (or epididymis in the male), on the surface of which it 

 breaks up into a number of fine fibres. Its upper end (gn'^) 

 accompanies the gonaduct in its course towards the complex of 

 accessory genital glands, and on its arrival into the complex 

 breaks up into a number of fine branches whose further course 

 I was unable to follow, but there is no doubt that they are 

 distributed to the different genital glands. This nerve corresponds, 

 without doubt, to the recto-genital nerve of other Streptoneura,. 



