112 THE VOYAGE OF H.M.S. CHALLENGEE. 



able nerve-stems, both of the vagus nerve and of the visceral nerves, by which this is 

 brought about, and that in longitudinal sections also (PI. XIV. fig. 5) the vagus nerve 

 may often be followed uninterruptedly for a very considerable distance backwards, being 

 applied upon the outer surface of the oesophagus, and only gradually dichotomising and 

 sending delicate nerve-fibres amongst the oesophageal epithelium {cf. PL XVI. fig. 1). 



Of the two sources of innervation of the intestine, the one by the nerve-stem directly 

 issuing from the brain-lobes (the so-called vagus nerve) is the most conspicuous, and can 

 be demonstrated in all species from Carinina to the more specialised Hoplonemertea 

 without exception. In Carinina it is represented in PI. VI. fig. 1, Nv; in this species 

 the visceral nerves (PI. XVI. fig. 1, vi.sy ; PI. XIV. figs. 3, 4, vi.n) have not been 

 definitely demonstrated as yet in either of the two available fragments. These latter 

 nerves are more easily detected in larger Schizonemertea, where the thick nerve-plexus 

 is itself so much more conspicuous. Cerebratidus cori'ugatus especially answers this 

 purpose. 



In the Hoplonemertea too the vagus is very evident, and already represented on 

 Quatrefiiges' figures (XXVIII); in Drepanophorus laiikesteri I saw its principal stem 

 running forwards towards the anterior oesophageal portion that passes under the 

 brain. 



In this species we find numerous thin nerves, both from the lower brain-lobes and the 

 lateral stems, further participating in the innervation of the oesophagus — a state of things 

 which may be directly compared to the mixed innervation described above for Cere- 

 hratulus corrugatus. 



I cannot as yet supply any definite statement regarding the innervation of the 

 posterior region of the intestine. 



NEPHRIDIAL APPARATUS AND BLOOD-VASCULAR SYSTEM. 



Our knowledge of the nephridia of the Nemertea is only of a comparatively recent 

 date. Though discovered by Max Schultze as early as 1851 in a Tetrastemma (XXXII), 

 the observations of this naturalist concerning the Nemertean nephridia were for a long 

 time wholly unjustifiably disregarded, and this general scepticism made me very careful 

 in formulating any definite opinion, wdien I also discovered in Schizonemertea separate 

 lumiaa (iv), which I could hardly account for in any other way than by regarding them 

 as parts of a nephridial system. 



This was afterwards more em^ahatically done by von Kennel (XVl), to whom is due 

 all the credit of having rediscovered the nephridia, and of having described their histo- 

 logical appearance in several diflerent genera. His results were later on confirmed by other 

 authors (ll, iii, xi). I liave afterwards observed and described (xil) a special modifica- 

 tion of the nephridial system in Nemertea, in which au indubitable internal opening is 



