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



has been acquired by two superposed layers of the basement membrane of Pelagonemertes 

 (PL VIII. fig. 13, B, B') ; the outer one being darker than the inner. I have no 

 explanation to offer of this phenomenon, nor of the fact shown by the same figure 

 (PL VIII. fig. 13) that the same phenomenon is repeated just below the basement 

 membrane, the jelly between the bundles of longitudinal muscles being much darker than 

 that which is found inside. The latter, into which the former gradually merges, is not 

 specially indicated in fig. 13. Mention ought here to be made of what is marked dr in 

 that figure, and what appears to be in several cases (PL VIII. fig. 5) a central cavity 

 enclosed by peculiar cells, of which the nuclei are specially distinct. I must leave it 

 undecided whether these structures, radially directed towards the surface of the body, are 

 the same as the masses dr (PL VIII. fig. 4), which I see in a glycerine preparation of the 

 integument made by Professor Moseley on board the Challenger from the fresh animals, 

 and also whether these structures might be looked upon as glandular, and comparable 

 to similar gland-masses in the jelly of Amphvporus moseleyi (PL XV. figs. 11, 12). 



That the course of the fibrds traversing the jelly is in no way strictly limited to 

 certain directions, but that we find them now parallel to the proboscidian sheath, now to 

 the intestinal wall, now convergingly directed against the generative ducts, is sufficiently 

 demonstrated in PL VIII. figs. 3, 8. A very large number are, however, radially directed 

 towards the surface, and though it was not observed in one section, it might perhaps be 

 possible to find dorso- ventral fibres uniting both surfaces. That the nerve-stems, spring- 

 ing from the lateral cords N (PL VIII. fig. 3), are indeed encased in a tubular space 

 bounded by darker stained gelatinous substance, is best seen in fig. 6 of the same plate, 

 as well as the fact that in the immediate neighbourhood cells and fibres (/) form part of 

 that substance. 



In the other Hoplonemertea this continuous jelly, though much less prominent, has 

 very much the same character as in Carinella, with the exception that no special tubi- 

 form tracts for the passage of nerves, &c, are as distinct as they are in Pelagonemertes. 

 The passage of radial fibrous tracts through the gelatinous tissue is, however, everywhere 

 demonstrable (PL X. figs. 1, 2), as is also the origin of these fibres out of cells (PL X. fig. 2), 

 and the continuity of the gelatinous stroma with that contained between the muscular 

 bundles of the body-wall. The Challenger Nemertea not offering anything very special 

 in this respect, I will postpone a more circumstantial discussion of this tissue for the 

 monograph which I am preparing for the Naples series. 



Similarly I may rapidly call to mind that, in the Schizonemertea, where this gelatinous 

 substance is best observed in the posterior region of the body, and better in large speci- 

 mens than in small ones (PL XV. figs. 7, 10), it offers the same characters. Anteriorly, where 

 the circumcesophageal blood-space is present, it does not play any conspicuous part ; pos- 

 teriorly, however, it carries not only the tubular continuations of this space (the three longi- 

 tudinal blood-vessels) but also the other internal organs, to all of which it is closely applied. 



