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12
et langt, rørformigt, gjennemsigtigt Legeme (det
contractile Kar), der gaar et Stykke bag paa Tarmen, hvor det
ender i en kolbeformig Blindsæk, Fig..27, g; fortil løber
det til Snabelens forreste Ende. hvor det deler sig, og
danner Karringen, som følger Tentakelkraven i alle dens
Bugtninger for at afgive Grene til Tentaklerne.
Retractorerne ere 4, hvoraf de to Bugretractorer ere
meget lange og tage deres Udspring med 3 Rødder fra den
forreste Del af Kropshulhedens bagerste Trediedel, Fig.
27, l, imedens Rygretractorerne udspringe fra det forreste
Parti af Kropshulhedens midterste -Trediedel, Fig. 27, h.
Strax bagenfor Spiserørets forreste Ende forene de sig og
danne ligesom en Skede om dette, idet de fæste sig som
sædvanligt paa Mundskivens Rand.
To Segmentalorganer, Fig. 27. i, der ere meget smaa,
omtrent 6mm langö og 2mm brede ved deres
Tilhæftnings-sted. Lidt bagenfor dette og paa den Side, som vender
imod Kropsvæggen, sees en liden oval, tragtformig Aabning,
Fig. 28, a, der fører ind til Hulheden.
Centralnervestrængen ligger langs Midten af Bugfladen
imellem begge Retractorerne og er temmelig tyk, Fig. 27,
k, 29, a. Den afgiver paa sit hele Løb en Mængde
Sidegrene, der som oftest udgaa afvexlende og tabe sig i
Huden. Strax bagenfor Mundaabningen deler den sig i to
Grene, Fig. 29, b, 6, der - slaa sig om Svælget for at komme
op paa Rygsiden, hvor de tabe sig i et aflangt Ganglion
(Hjerne), der er ligesom indsnøret paa Midten, Fig. 29, .c,
og som ligger imellem begge Rygretractorerne, just paa det
Sted, hvor disse forene sig. Saavel fra Svælgringen som
fra Gangliet udgaa flere Grene, Fig. 29.
Centralnervestrængen og dens Grene ere omgivne af
en Bindevævsskedé, der danner det egentlige Neurilem.
Paa hver Side af Nervestrængen iagttages
etMuskel-baand, der er omtrent ligesaa bredt, som selve
Nervestammen; det strækker sig fra Svælgringen op til
Nervestræn-gens bagerste Ende og er fast forenet til den udvendige
Sideflade af Neurilemmet. Dette Muskelbaand bestaar af
stærke Muskelfibre, hvoraf enkelte strække sig ud over den
Del af Sidegrenene, der ligger frit i Kropshulheden. men
forsvinde efterhaanden som Grenene gaa ind i Muskellagene
eller tabe sig i Huden.
Dr. Théel1 har iagttaget og beskrevet lignende
Muskelbaand hos Fhascolosoma Strombi.
Intet Spor til Kjønsorganer har været at opdage.
Farven.
Selve Kroppen olivengrøn, mørkere paa den forreste
og. bagerste Del. Snabelen noget lysere; dens forreste
1 Hjalmar Théel. Récherches sur le Phascolion Strombi. Kongl.
Svenska Vetenskaps-Akademiens Handlingar, B. 24, No. ’2.
the right, is seen a long, tubular, translucent body (the
contractile vessel), protending a short distance back on the
intestine, where it terminates in a cæcum, cucurbit-like in
form, fig. 27, g; anteriorly, it passes forwards to the
extremity of the proboscis, forming there the vascular ring, which
accompanies the tentacular collar in all its windings, and
sends off branches to the tentacles.
Number of’ retractors 4: two of them, the ventral
retractors, which are exceedingly long, • take their origin,
with 3 roots, on the anterior portion of the posterior third
of the perivisceral cavity, fig. 27, I, whereas the dorsal
retractors originate on the anterior portion of the medial
third of the perivisceral cavity, fig. 27, h. Immediately
posterior to the anterior extremity of the oesophagus, the
4-retractors unite, and form, as it were, a sheath for that
organ, being as usual attached to the margin of the oral disk..
Two segmental organs, fig. 27, i, exceedingly small,
about 6mra long and 2mra broad at the point of attachement.
A little posterior to the latter, and on the side facing the
wall of the body, occurs a small, ovate, funnel-shaped
aperture, fig. 28, a, leading down into the cavity.
The central nervous’ chord, which is comparatively
thick, extends along the middle of the ventral surface,
between the two ventral retractors, figs. 27, k; 29, a.
Throughout its entire course it sends off numerous
subsidiary branches, which, as a rule, issue alternately, and
coalesce with the skin. Immediately posterior to the
buccal aperture, it divides into two branches, fig. 29, b, b,
which, winding round the gullet, reach up to the dorsal
surface, and are there lost in an oval-shaped ganglion
(brain), — constricted, as it were, in the middle, fig. 29, c,
— lying between the two dorsal retractors, in the exact
spot where they unite. Both from the pharyngeal ring
and from the ganglion, proceed several branches, fig. 29.
The central nervous chord and its branches are
in-vaginated in a sheath of connective tissue, which constitutes
the true neurilem.
On either side of the nervous chord is observed a
muscular band, about equal in breadth to the nervous
trunk itself, extending from the pharyngeal ring «to the
posterior extremity of the nervous chord, and firmly affixed
to the exterior lateral surface of the neurilem. These
muscular bands consist of strong muscular fibres, some of
which protend beyond the portion of the subsidiary branches
lying free in the perivisceral cavity, but are gradually lost,
as the branches pass into the muscular layers, or coalesce
with the skin.
Dr. Théel1 has observed and described similar
muscular bands in Fhascolosoma Strombi..
Of generative organs no trace could be detected.
Colour.
Trunk olive-green, both extremities of a darker shade.
Proboscis somewhat lighter; its anterior extremity, for
1 Hjalmar Théel. Récherches sur le Phascolion Strombi. Kongl.
Svenska Vetenskaps-A kademjens Handlingar, B. 24, No. 2.
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