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Their protoplasm has, usually, a prominent globulous structure (Pl. VIII, fig. 12) which is especially observable in M. graffi,
M. giganteum, M. carpenteri etc. I think, that these globules must be absorbed nutritive substance. Cells of M.
cirriferum are, in fresh state, blackened by osmic acid, which would appear to show that they contain fat. In M. cirriferum, the
epithelium is higher on the dorsal side of the branches than on the ventral side. A similar tendency can, usually, be traced in the other
species; the cells, however, vary, in a great degree, in length, as well as in form and appearance, vide Pl. VIII, fig. 12 and 13.
I think that this variation is, partly, occasioned by the cells being, more or less, filled with nutritive substance. On the outer
side of the membrane surrounding the intestinal branches, muscular fibres are, frequently, observed, one end of which is
secured to the membrane. In these membranes, trans-sected canals are also observed (fig. 12, a.).
The rectum is divided from the stomach by an annular protuberance in the epithelium, caused by the epithelial
cells in the posterior part of the stomach being very long and prominent, whereas, in the anterior part of the rectum, the
cells are very much flattened, especially on the dorsal side; just in rear of the before mentioned protuberance, two oviducts
open into the rectum which, therefore, becomes transformed into a cloacal canal (figs. 20 and 21). At the posterior extremity,
close to the anal aperture, a third dorsal oviduct opens. The epithelium is, to a certain extent, ciliated, especially in the
posterior end. In the posterior portion of the cloacal canal, in most species, the epithelium forms longitudinal ridges. The
cloacal canal is surrounded by a muscular layer, considerably less developed and continuous, however, than that of the stomach.
Glandulous tissue surrounding the alimentary canal. I have observed, in M. graffi especially, a peculiar tissue
surrounding the posterior part of the stomach, on the dorsal, as well as 011 the ventral, side (Pl. II, fig. 3, m. v. k.) and which is
extended over the anterior part of the rectum. This tissue has a remarkable structure which is seen illustrated in Pl. VII,
fig. 23. Numerous large nuclei are visible, but, at same time, a great many minute corpuscles, or nuclei, can be observed
destributed throughout the entire tissue. I believe the function of the tissue must be secretive, but I have, however, not
detected any secretory opening into the stomach or rectum. In the other species examined, a similar tissue is but little
developed. In the connective-tissue surrounding the stomach, nerve-cells are, frequently, observed; these, I think, belong to a
sympathetic nervous system which I have, however, not submitted to exemination.
Genital organs.
Female genital organs. The ova are, I think, derived from the epithelium of the body-cavity; remnants of this
epithelium are only found, now, in the mesial dorsal portion of the body-cavity, the uterus and approximate parts; the
epithelium occurring here is ciliated, and flattened (Pl. VII, fig. 27). On the dorsal side of the stomach, one or two pairs of
organs occur (PL II, fig. 6 and 15, ov.r., Pl. IX, fig. 23 ovr.); these organs are situated in, more or less open, branches
issuing from the uterus, and consist of crowds of small cells with dark staining nuclei and nucleoli (Pl. VIII, fig. 23). I have
found ova close to these organs, vide fig. 23 ov. I consider these organs to be traces of the primordial ovaries which have,
however, degenerated, the epithelium of the body-cavity acquiring the function of producing ova. There are three oviducts.
One dorsal oviduct, which has been described by Graft", has a very minute aperture which, in sections, is very difficult to
distinguish. I am not certain whether in some species, e. g. M. giganteum, the aperture is not separated from, and situated
at the side of the cloacal aperture. Besides this dorsal oviduct, there are two lateral, or ventral, oviducts issuing from the uterus
and passing down, one on each side of the stomach, towards the ventral side, vide Pl. I, fig. 11 ovd. here, they, pass
backwards, and open into the anterior end of the cloacal canal, vide Pl. I, fig. 8, Pl. IX, fig. 10 and 23. The epithelium of these
oviducts is much ciliated (Pl. VII. fig. 26); it is of a secretory nature, and mucous globular secretions of variable size are often
observed in it, vide PL VII, fig. 25, a. Besides being oviducts, these ducts may, probably, be regarded as respiratory ducts.
The cilia at the openings into the cloacal canal are, usually, found to be directed inwards into the ducts. From the
descriptions of Graff and previous writers, we know that seawater passes through the anal opening into the cloacal canal; may it not
pass thence into the oviducts (??). On the assumption that the function is respiratory, the meandering course may also be
explained but it" the function is, only that of oviducts, the latter is difficult to account for. The ova, usually, have a globular form.
In the nucleus, I have, frequently, observed small globular bodies; whether they are analogous to those of Amphibia and
Insects described by Will1), as Beard supposes, I have had no opportunity of examining.
Male genital organs. The testes are, principally, situated between the alimentary canal and the nervous system, but
many of their branches are, however, situated between the lateral branches of the alimentary canal. I have observed in one
species, M. cirriferum, several branches of the testes extended to the ectoderm of the dorsal side and the margin of the
body, vide Pl. II, fig. 5 t. I have observed, in other species, small isolated testes under the ectoderm in the margin of the
’) Zool. Anz. 1884, No. 167, 16S.
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