REPORT ON THE NEMERTEA. 63 



It will be well to consider this connective tissue more closely before we pass to the 

 description of the muscular layers of the body-wall. From the foregoing it may already 

 be inferred that there is a direct continuity between the different parts of this gela- 

 tinous tissue, be it situated close to the intestinal epithelium or to the integument, and 

 that this continuity is more or less completely interrupted by the muscular layers. 

 We may thus conclude that it will be most prominent in those species that have the 

 muscular body-wall reduced to a minimum, whereas it will be hardly visible in species 

 that have a very strongly and massively developed musculature. This is indeed the case, 

 Pelagonemertes offering a very striking example of the first category, Carinina of the 

 second. 



Although the latter species is by far the most primitive, I would hesitate very much 

 in at the same time regarding the relation of the gelatinous tissue to the body-muscu- 

 lature of this deep-sea form as typically representing the original arrangement. Both 

 species mentioned represent an extreme ; the normal starting point may be more easily 

 derived -from what we find in Eupolia and in most Hoplonomertea. It then becomes 

 obvious that our gelatinous tissue, though uniform and continuous, still appears in three 

 principal modifications, which, however, are often connected by transitional phases having 

 the characteristic features of more than one of these modifications. 



The first of these modifications is found between the muscles and the integument, 

 the second in the midst of the muscular bundles, the third between the muscular invest- 

 ment and the internal organs. 



The first modification just alluded to appears in Carinina (as also in Carinella and 

 other Palseonomertea not collected by the Challenger) as a wholly homogeneous base- 

 ment layer, on which the deeper cell layers of the integument are implanted, partially 

 honeycombing it in the way above noticed. It is strongly stained by picrocarmine, and in 

 Carinella traversed along circular and longitudinal tracts by nervous tissue. In Carinina 

 the corresponding tracts are still situated in the deeper layers of the integument itself. 

 Nuclei are very rare. What is a distinct basement layer in the more primitive Palseo- 

 nemertea just named, retains this character with but little change in the Hoplonemertea. 

 One change which is revealed at first sight is a distinct though exceedingly fine stratifica- 

 tion, that becomes apparent in the basement membrane of nearly all Hoplonemertea. 

 Along with this we very often find included in the Hoplonemertean basement layer 

 distinct and sometimes numerous nuclei. The other inclusions in it, as they are 

 figured on PL X. fig. 1, B, appear to be parasitic unicellular organisms infesting 

 this particular specimen (see p. 49). Besides the exceedingly fine stratification which is 

 parallel to the surface of the body, and which is often thrown into wavy folds, there are 

 numerous radial tracts that would seem to transverse this basement layer, but are often 

 only due to slight differences in texture and coloration, or to hardly susceptible folding or 

 contraction (PL VIII. fig. 13). Where actual radiating fibres can be demonstrated, they 



