REPORT ON THE ISTEMERTEA. 99 



similarly more or less a repetition of the same arrangement in the body-wall (PL XV. 

 fig. 2, a', /3', npl, y'). 



In addition to the peculiarity just described, there is another morphological consider- 

 ation which tends to show that this interpretation of the significance of the proboscis 

 is indeed the right one. When we consider a horizontal section through the region of 

 insertion of the proboscis in the head (PI. III. fig. 5), we see that in Carinina the mode 

 of fixation of the proboscis is exceedingly simple, its longitudinal muscular coat being in 

 direct continuity with the longitudinal muscle-layer of the body-wall. Somewhat in 

 front of the transverse cephalic grooves, about on a level with the anterior brain-lobe, 

 we see certain of the fibres of this longitudinal coat, instead of pursuing their course 

 onwards towards the tip of the head, bending inwards, traversing the space which I have 

 termed (XIII, xv) the archicoele, and then rimning backwards as the longitudinal fibres 

 of the proboscis. Other fibres, parallel to those just referred to, do not contribute 

 towards the formation of the proboscis, but continuing in their original direction, take 

 part in the formation of the muscular wall of the head (PL III. fig. 5). It certainly 

 deserves remark that the same comparatively simple arrangement is met with in the 

 much more highly differentiated Hoplonemertea, as a glance at fig. 3, PL X. will show. 

 There, too, the longitudinal musculature (a) of the body-wall is partly continued towards 

 the tip of the head, where it partly bends round and largely contributes to the formation 

 of the muscular layers of the proboscis. I suppose this way of stating the facts is more 

 in accordance with their actual relations, than to say that the longitudinal musculature 

 of the proboscis is internally inserted upon that of the body. Here also the direct 

 continuity of body-waU and proboscidian-wall, the latter appearing merely as an inverted 

 portion of the former, is forced upon our attention, as is in the same way the direct 

 continuity of the exterior integument J, through that of the rhynchodajum Rh to that 

 which clothes the proboscis itself, and which on the eversion of that organ forms the 

 exterior surface. 



We must now consider these difi"erent parts more in detail. Commencing with the 

 rhynchodseum {cf. p. 8)^ we find in the Palseonemertea and Schizonemertea its walls bathed 

 by the blood-spaces in the head, as may be gathered from a comparison of the figures in 

 Oudemans' paper (XXVIl) on the blood-vascular system. This is no longer the case in 

 the Hoplonemertea, where these blood-spaces are replaced by the distinct vascular loops. 

 The proboscidian walls, fusing anteriorly with the musculature and the external epithe- 

 lium of the head, are difi'erent in the difi"erent subdivisions. Contractile fibres and cellular 

 elements, the materials of which the rhynchodoeum is built up, are present in Carinina 

 in quite a difi'erent relation from that in which they occur in Cerehratulus or Amphvporus. 



In Carinina, as a glance at PL III. fig. 5 wiU show, it is the cellular elements {APe) 

 that are extremely preponderant. These cells are vacuolated, more than one layer thick, 

 difi'erent in aspect from the true proboscidian epithelium, and held together by a fibrous 



