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



(cf. PL VI. figs. 7, 8 ; PL XIV. figs. 6-8, 11). What the physiological meaning of this 

 glandular investment may be must remain unsolved for the j)resent, although we will 

 return to this question further on. Carinina demonstrates that, as the brain-lobes are 

 direct derivatives of the integument, so is the glandular investment of the posterior one. 

 I may here note that, in studying the development of Lineus obscurus, I have (XIV) 

 been able to determine the fact that the glandular investment and the nerve-cells of the 

 posterior brain-lobes also arise in that species out of the same mass of embryonic 

 cells. Moreover, I must add that the glandular significance of this investment was for 

 the first time more emphatically brought forward by Dewoletzky in a short notice on the 

 Nemertea (II). Although I cannot accept all the conclusions to which this naturalist 

 arrives with respect to the apparatus of which we are here treating, and must demur 

 when he rejects the specially adapted respiratory significance which the brain canal must 

 necessarily have in very many species, still it is only fair to call attention to his inquiry 

 into the nature of this cellulo-glandular investment. 



The only point which has still to be noticed, and which is partly a repetition of what 

 has been already described in the paragraph on the nervous system, is the fact of the actual 

 observation by myself in DrepanopJiorus lanhesteri, from the Challenger collection, of 

 the passage of the contents of part of these glandular investing cells into the lumen of 

 the canal (PL XIV. fig. 10). Moreover, one point should not be lost sight of, viz., that 

 between the glandular cells that form an actual investment of the posterior lobe (and 

 which in Carinina could be identified with the deeper glandular structure of the integu- 

 ment) and the actual integumentary glands, there exists in Schizonemertea a constant 

 and considerable difference, even with respect to the affinities for staining reagents, and 

 still more in the general aspect. The case of Carinina is on this account all the more 

 interesting. We must only be careful not to look upon the exceptional case which I was 

 able to observe and to figure (PL XIV fig. 11, gl), in which an additional glandular (1) 

 ring surrounds the ciliated canal after it has passed out of the brain-lobe on its way to 

 the exterior, as one of transition. I hardly think that this special adaptation, which has 

 been already noticed above (p. 60), pertains to the layer of the deeper skin-glands ; and 

 though I am not prepared to offer a definite opinion, I am much more inclined to compare 

 this curious accumulation of distinct and nucleated cells with a similar accumulation 

 which we have also noticed in Carinina, and have there encountered more peripherally 

 but still surrounding the ciliated canal (PL VI. figs. 1-3). In either case the physiological 

 significance of the arrangement cannot at present be decided. 



And to a certain extent this may also be said to be the case with respect to the whole 

 of the posterior brain-lobe. As long as it went by the name of side-organ — which, how- 

 ever, did no justice to its intimate connection with the brain — it was generally regarded 

 as a specific sense-organ of unknown function (Quatrefages, MTntosh, &c). Later on I 

 published a paper (IX) in which the attempt was made to show that, in a very large number 



