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



coating, wliich is attached by radial fibrous bands to the cephalic musculature. The 

 rhynchodseum is thus suspended in the cephalic blood-space, as was formerly (IX) 

 described by me in Carinella. 



The histological difference between the vacuolated cells of the rhynchodseum of 

 Carinina and the cells of the outer integument, is less than that between the former and 

 the epithelium of the proboscis proper. 



A comparison between figs. 3, 4 of PL III., fig. 1 of PI. IV., and figs. 1-3 of PI. VI. will 

 sufficiently demonstrate this, vacuolated cells playing a very prominent part in the outer 

 strata of the integument in Carinina. Still the three epitheUa (external, rhynchodseal, 

 and proboscidian) are immediately contiguous, the passage from the one to the other 

 being gradual and only in the latter case relatively abrupt. 



In the rhynchodjeum of the Schizonemertea and Hoplonemertea the cellular and ciliated 

 layer of the rhynchodseum of the earliest Palseonemertea has been relegated to the back- 

 ground, and the whole has become more a muscular sheath, in which the muscles have, 

 however, a diff"erent arrangement in the first and in the second group. The increase in 

 muscularity is in the Schizonemertea more a regular thickening of the fibrous investment, 

 whereas in the Hoplonemertea it is much more massive in one region than in the other. 

 In this way an annular and massive muscular sphincter (as it may be adequately termed) 

 arises in the posterior part of the rhynchodseum (PI. X. fig. 3, Sp. Pr.). 



In this muscular sphincter longitudinal and circular fibres are very intimately inter- 

 woven, more or less in basket fashion, as indicated in the figure. Moreover, the 

 connection with the general musculature of the head is again brought about by radial 

 bundles, also visible in the figure. 



Of the Schizonemertean rhynchodseum no special figure is given ; it answers to the 

 short description which was given above, it can be well observed in several figures in 

 M'Intosh's monograph, and, like the rhynchodseum of the other groups, it reaches back- 

 wards just as far as the implantation of the proboscis in the musculature of the head. 

 The epithelium of the rhynchodseum is in most cases distinctly ciliated. 



The proboscis itself has been the subject of so detailed study and so elaborate 

 description by M'Intosh and other investigators, that I must necessarily restrict myself 

 to those few points on which the Challenger material furnishes certain deviations or 

 additions. 



The inner epithelium of the proboscis of Carinina shows considerable difierenccs 

 according to the region under observation. In front there are papillse of a more or less 

 arborescent shape, on which a coating of fairly large cells, with distinct nuclei, and 

 partly vacuolated, is present. Posteriorly the cells are lower and more closely set (PL 

 III. figs. 1, 2, Pc). This may be partially the result of a difi"erent state of contraction, 

 by which the anterior portion is thrown more into folds. 



The difference is, on the other hand, further accentuated by the presence of a con- 



