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



substance and fills up the central area of the body in transverse section to an unusual 

 extent, as pointed out by Professor Moseley. 



" Besides the organs mentioned by this author within the body-cavity, a large number 

 of granular nerve-cords run outwards to the surface (muscular wall), besides fine fibres, 

 which are very apt to assume a coiled or zig-zag appearance. Some of these much 

 resemble blood-vessels, but they are probably nerves, and they divide into fine branches 

 towards the muscular coat. 



" The proboscidian sheath or chamber is very large, and its anterior aperture would 

 seem to be unusually distinct. The structure of the parts in unrolling of the organ is 

 the same as in the others, and the wall of the chamber presents continual circular internal 

 longitudinal fibres; the posterior region of the proboscis is firmly fixed as usual to the 

 internal wall of the proboscidian sheath at its narrow posterior end. The fibres of 

 attachment are short, so that the cul-de-sac of the posterior chamber is brought close to 

 the surface of the wall of the sheath. From the appearance of the parts posteriorly, it is 

 possible that the region is in process of repair after laceration. Indeed, it is not unlikely 

 that both anterior and posterior ends can easily be repaired after rupture, and that might 

 account for the absence of eyes (see Lesson's Pterosoma, 'Voyage of the Cocpuille'). 

 Such gelatinous forms are especially prone to rupture, and sufficient is known of the 

 recuperative power of the Nemertean to render repair rather than permanent injury the 

 rule. The proportionate size and firmness of the proboscidian chamber, with its glistening 

 internal surface, are certainly remarkable, and, on the whole, my impression is that the 

 form is incomplete posteriorly." 



All the fragments of Pelagonernertes that came into my hands were carefully treated 

 with staining reagents, hardened, imbedded and sectionised. The sections were all trans- 

 verse. PI. VIII. fig. 3 represents one of the average sections with parts of all the important 

 organs imbedded in the common gelatinous basis. No sufficient sections of the brain 

 were available, nor were distinct traces found of a nephridial system. The integument 

 was in most parts of the surface wholly deficient ; in a few others its general correspond- 

 ence in transverse section with what is typical for the Hoplonemertea could be verified. 



Certain other striking particulars, also visible in this section, and on the whole only 

 confirmatory of what we already knew by Moseley's and MTntosh's observations, are 

 (l) the absence of a dorsal median blood-vessel; (2) the ventral openings of the generative 

 sacs; (3) the numerous transverse fibres, both contractUe and nervous, running in 

 different directions through the body -jelly. Further, it may be observed, even with a 

 rather low power, that each of the ripe ova is surrounded by numerous small follicle cells 

 (PL VIII. figs. 3, 11), and that the nucleolus is often only represented by very numerous 

 small chromatin spheres. 



By the aid of stronger powers the details also represented on PL VIII. by 

 figs. 4-13, can be more fully studied, and of these mention will successively be made in 



