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76
The body-cavity and the connective-tissue.
A definite body-cavity is, in my opinion, not present; what may be considered as rudiments of it, are the cavities
in which the ova are situated. These cavities may be quite filled with ova, but sometimes they are nearly empty and have
ova situated in an interrupted layer along the walls. The ovaries are derived from the epithelium of the body-cavity, and
this epithelium is, now, only remnant in some particular places, especially in the - uterus« and adjacent parts on the dorsal
side, where it can be seen as a thin ciliated epithelium, vide Pl. VII, fig. 27.
The body-parenchyme consists of a reticular connective-tissue. The size of the meshes, in this tissue, varies in
the different parts of the bod)’. The nuclei are oblong and have a granular appearance, the granules appearing as thickenings in
the chromatic structure, vide Pl. IX, fig. 15. The nuclei are, usually, situated in the fibres forming the meshes, and consequently,
not in the meshes themselves, as described by Graft". I have only observed such a nucleal situation in some special parts
ol the body, particularly in the connective-tissue of the anterior proboscis (Pl. IV, fig. 6 and 7), I have not observed
»Rundzellen which, according to his description, is identicaj with »den durch die Leibesflüssigkeit frei im Körper
umher-getriebenen Blutzellen , and from which, also, the ova are supposed to be derived, nor have I met with connective-tissue
nuclei of the globular form described by him.
Muscular system.
Pl. VIII, fig. 26 illustrates some dissociated dorso-ventral muscular fibres. The nuclei are, usually, situated in
protoplasmic prominences at the side of each fibre. The extremities of the muscular fibres are divided into several branches,
between which protoplasmic remnants, are seen (probably of connective tissue). Sometimes the nucleus is situated more
towards one of the extremities (b); I have even seen it situated between the branches (a).
Segmental glandulous sacks ( Suckers ).
What previous writers have called suckers« are not, really, such, but ciliated glandulous sacks, as illustrated in
Pl. VIII, fig. 19 and 20. There are no muscular walls such as Graft" has described. The inner walls consist of a glandulous
tissue, with large cells situated in one, or several layers; this tissue is covered by a ciliated cuticle, which is striated by the
cilia penetrating it into the tissue, vide figs. 19 and 20. Only a few muscular fibres occur in the walls of the sacks, and those
»
are, usually, dorso-ventral muscles which penetrate through the glandulous thissue and are secured to the cuticle by their
extremities, vide fig. 20, m. In M. glabrum, the glandulous tissue is separated from the surrounding connective-tissue by a
cuticle, on whose exterior side several muscles are situated, and I have not observed such a clearly defined cuticle in the other
species examined. In the surrounding connective-tissue, vacuoli frequently occur. Among the glandulous cells, connective-tissue
nuclei can be seen; this is especially the case in M. graffi, and M. giganteum. — The openings of these sacks are, more or
less, prominent in the various species, and the thickness, of their oral margins, also varies very much, vide Pl. VIII, fig. 19 and 20.
The form of the opening is, in some species, circular (e. g. M. cirriferum fig. 22) and in others, oval (e. g. M. giganteum fig. 21).
The openings are provided with sphincters, which vary in development in the various species; in some species they are few
in number, and thick (e. g. M. cirriferum, fig. 20, sph.) whilst, in other species the)’ are more numerous, but are, then, less
developed in thickness (e. g. M. giganteum. fig. 19). Round the openings radial fibres, also, occur, whose function is to act
as dilatatores, vide fig. 18, m, m’; fig. 21 and 22.
What is the phylogenetic development of these organs? Are they homologous with the segmental organs,
or with the dermal glands of the Gephyreans for instance, or perhaps, with the trachea of the Arthropods? In the present
state of our knowledge we are unable to determine this question. The greatest disagreement, between the organs we have
described and the segmental organs of the Annelids, consists in the fact that in Myzostomida they do not communicate with
the body-cavity. This cirrumstance may, however, be explained by the degeneration, or partial disappearance, of the body-cavity,
during which process the segmental organs have become transformed into these we find in the present Myzostomidae. Whether
these glands are related to the »segmental organs described by Huet1) as existing in the greatest part of the terrestrial
Isopods, is not easy to determine. They agree in not having any open communication with the body-cavity, but in their
structure, otherwise, they seem to be quite different.
’) Huet: Sur l’existence d’organes segmentates chez certain Crustacés isopodes. Coniptes Rendus 1882. T. 1. p. 810—811. Regarding
these glands he states; »Iis manquent a la tete. Iis s’ouvrent a la partie supérieur des epimires de chaque coté par une ouverture en crible. Cela fait
done pour les septs anneaux du corps, quatorze glandes«...... Certains des elements cellulaires niesure un cinqui^me de millimetre .... Entre eux
s’étend une sorte de vestibule d’ou part un conduit rempli par la mature .sécrétée.« According to that description, it would appear that these glands have
more resemblance to the parapodial ganglia of M. graffi.
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