54 THE VOYAGE OF H.M.S. CHALLENGER. 



above — remains the same in the adult, and we have in this more superficial situation of 

 the central nervous system one of the surest indications of the more primitive position 

 that ought to be assigned to Carinina and the allied genera, when compared with the 

 other Nemertea. 



The intermixture of integumentary and nervous tissue is none the less evident 

 in the medio-dorsal longitudinal nerve than in the lateral stems. The first named nerve, 

 which in former publications (IX, X) I have, not wholly adequately [cf. p. 132), desig- 

 nated as the proboscidian-sheath-nerve, can readily be distinguished in my transverse 

 sections of Carinina as a delicate stem. It is not situated, as in the Schizonemertca, just 

 outside the circular and below- the outer longitudinal muscular coat, nor, as in Drepano- 

 2)Jiorus, Amphiporus marioni, &c., below the basement membrane just outside the same 

 circular muscular coat, but it lies in this case actually outside the basement memhrane, 

 and forms part of the deepest layer of the celhdar integument. Further, a plexus-like 

 distribution of nervous tissue between dorso-median and lateral nerve-stems obtains in 

 this species, as was more fully described elsewhere for the Schizonemertea, connecting 

 the three longitudinal stems and spreading round the body as a cylindrical investment. 

 It must be remarked that this plexus-like arrangement is thus necessarily situated in the 

 very layer of the integument with which we are occupied, and it may be added, that in 

 numerous transverse sections of Carinina the presence of fibrillar nerve-tracts in this layer 

 can be easily demonstrated, and these exactly resemble those that are met with in the 

 nervous plexus of Schizonemertca. This plexus has, since my first notice of its presence 

 (IX, x) been again observed by Dewoletzky (H) and other naturalists, and will be more 

 fully discussed in a succeeding paragraph. 



The plexus here alluded to merges into the lateral nerve-stems. I may here once 

 more emphasize the fact that the whole system lies outside the basement memljrane. At 

 the same time, however, the lateral stems would seem to be separated, though very 

 incompletely, from the integument by bundles of fibres which bind them down to the 

 underlying layer of circular fibres (PI. III. figs. 7, 8.) 



In the vicinity of the brain-lobes it is impossible to distinguish between the cells 

 of the deepest integumentary layer and the nerve-cells. With respect to this layer I 

 have further to state that its nuclei are less conspicuous, its cells paler, and the boundary 

 lines of the latter less easily distinguished than in the other layers. Extremely delicate 

 fibrillar tracts were already noticed as occurring in it. 



The next layer to this, when we pass outwards, is the glandular layer of the integu- 

 ment. It is the thickest of the four, being alone often as massive as the three others 

 taken together. The large, flask-shaped, and tubular glands it encloses contain a thick 

 granular secretion, which is partly stained brownish-yellow, partly dark red in my pre- 

 parations (PI. HI. figs. 3, 7, 8, gi ; PI. IV. fig. 1 ; PI. VI. figs. 1-3). The ducts leading 

 to the exterior penetrate the two outermost layers. The presence in the most peripherally 



