// 



S(->mc other organs, which ha\'c also been compared with the .segmental organs, are the antennal glantls of some 

 Crustaceans, and the shell-glands of Co])opoda and I'hyllopoda ') These also agree in having no open communication with the 

 bod\--ca\it_\-. Before coming to a decision, on this question ot the phylogenetic origin of these segmental glands in Myzostomida, 

 it would lie of utmost interest to have elucidated, whether it, really, is the case, as Graft" states, that »suckcrs'< are not 

 present in man)" species, or whether, at all events, traces of these glands do not exist in all species. 



Hook Apparatus. 



The hook-apparati of the Mw.ostomidae have, I think, an ectodermal origin. They consist of: a) the liooks, (chiet 

 hook, supporting rod, and reserve hooks) with their muscular system, and b) the glandular mass surrounding the hooks. The 

 hooks are not. as Graft" states in his monograph,'^) hollow, but consist of two layers; an outer, somewhat homogeneous, layer, 

 and an inner one composed of a fibrous substance. The outer layer has a j-ellow colour and is very slightly staining; it is 

 \'ery thin at the base of the hooks, Init increases, gradually, in thickness towards the extremit)-, and the acuminate extremities 

 of the hooks become formed, thus, almost exclusively, by this layer, and acquire, also, a more intense yellow colour, especially 

 in the more developed hooks. The inner fibrous mass consists of colourless fibres, w'hich are thickest in the centre of the 

 hook and, in transverse sections, exhibit a distinct hexagonal form, vide PL \'II, fig. ig. Towards the outer layer these 

 hexagonal fibres become so minute that they are with difficult)- distinguishable. This fibrous mass is, usuall)'. vividl)- stained 

 by colouring reagents. The structure of the supporting rod is similar to that of the hooks, and the manubrial plate is composed 

 of the homogeneous yellow substance of the outer la)'er. I have, frequently, observed at the upper extremit)' of the supporting 

 rods, large unipolar cells, with their prolongations directed towards the extremity of the rod (PI. MI, fig. 22, a, b.), but I 

 have been unable to determine in what manner these prolongations terminate, or what is their ph)'siological function. 



The glani^lular mass surrounding the hooks has, usuall)', a considerable volume, and this is especialh' the case 

 in M. giganganteum; in it, it is divided into two parts, one surrounding the hooks, and the other extending towards the centre 

 of the bod)', and in this there are vacuoli communicating with the canal in which the chief hook is situateil. The glandular 

 mass is composed of cells having a varial)le form and appearance. Most of them are elongated, antl have a fibrillous proto- 

 plasm (PI. VII, fig, 28, a.); these are, I think, the true glandulous cells. Some cells have a more globular form, also furnished 

 with prolongations (PI. VII, fig. 28, c.) I have observed in the canal encompassing the chief hook, in some species, large globular 

 cells, situated in a la)'er surrounding a la)'er of smaller elongated cells, vide PI. VI, fig. 6, c. and h.k. In the glandular 

 mass surrounding the canal of the chief hook, I have, frequentl)', observed, especialh' in M. graffi, deposits, having the form 

 of small elongated refracting corpuscles. The cavities of the glandular mass communicate with the external sea-water by 

 means of the canal of the chief hook. 



Alimentary Canal. 



The alimentar)' canal ma)' be considered as consisting of 3 parts viz. i The proboscisdeai canal with oesopha- 

 gus. 2) The stomach. 3) The intestinal branches issuing from the stomach. 4) The rectum and cloacal canal. At the 

 posterior extremity of the proboscis there is, usuall)-, a very short oesophagus, divided from the stomach !>)• an annular con- 

 striction ; but in some species, however, this oesophagus is relative!)- longer, as Graft, also, states, and this is the case in M. 

 carpenteri, vide PI. IX, fig. iS. The epithelium of the oesophagus forms a transition between the epithelium of the posterior 

 part of the proboscideal canal and that of the stomach; it is not ciliated; large cells are situated in the epithelium as well as 

 in the subjacent connective-tissue. 



The stomach is divided b)- a muscular annular constriction into two parts; an anterior portion — the true sto- 

 mach; and a posterior portion — the intestinal division — from which the lateral branches issue (PI. IX, fig. 17 — 20). In 

 M. carpenteri, the anterior portion is divided into two parts b)' another, not so prominent, annular fold. The epithelium, 

 in both portions of the stomach, is cylindrical and ciliated, an<l the cilia are especially long in the anterior part. Xo 

 such rule, as is laid down b)- Beard (loc. cit. p. 550), regarding the length of the cells can be established. In all [larts of 

 the stomach the cells vary, ver)' much, both in length and in form. In the connective-tissue walls of the stomach, annular 

 (retractores) as well as radial (dilatatoresj muscles occur (PI. I.\', fig. 22'. There are, usuall)', three intestinal branches, but in 

 M. giganteum, and x\I. gigas, there are onl)' two. The epithelium of the branches is, generall)', cylindrical, but not ciliated. 



1) Grobben: Die Antennenclriise der Crustaceeu. .\rb. Zool. Inst. Wien. Bd. III. 1880. See .ilso with reference to this. — Ilmk: Koi>ort 

 on tlie Cirripedia. Zool. Chall. Exp. I'art XXVIII, 1884, p. 26. 



■-■) In his Report on the Challenger-Myzostomida (Zool. Chall. Exp. Part. XXVII. 1884'. Graff says however: »It appears .also that the column 

 of the hook .and manubrium are not as I formerly thought, hollow, but in many species, at le.ast, solid. 1 



