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10
. Det indre Skelet.
Kalkringen er temmelig rudimentær, ligner vistnok
meget Kalkringen hos Elpidia og Irpa; men er baade langt
smekkrere og ikke saa inderlig sammenbunden, som
hosdisse. Den dannes af 5 Stykker, Tab. III. fig. 27, der
nærmest maa svare til Radialstykkerne hos andre
Holo-thurider. Ethvert Stykke, der er omtr. 1,5"" langt, har
et næsten firkantet Midtparti, Fig. .28, a, som er 0,068""
bredt og ikke fuldt saa hojt. Dette Midtparti er ligesom
delt i to Dele. en forreste, der er smalest, og en bagerste.
Fra den forreste Del udgaa 6 Stave, hvoraf de to hæve
sig skraa fortil og opad imod Spiseroret, og ende svagt
kølleformigt, Fig. 28, b, b; de øvrige 4, der hver deler sig
et Stykke ovenfor Udspringet i to Grene, Fig. 28, c. c,
hæve sig bagtil og opad, og synes at følge Tentakelkarrene.
Fra Midtpartiets bagerste Del udgaa paa hver Side 4 lange
Stave, Fig. 28, d, d, d, d, der ligesom straale ud til
Siderne, og hvoraf den længste løber noget paaskraa henimod
Enden af den tilsvarende Stav paa det nærmest
tilgrænd-sende Kalkstykke. Fig. 27, a, a. Enderne af disse Stave ere
bladformige, og forsynede med Indsnit og Huller. Fig. 28. De
her nævnte Kalkstare fra .Midtpartiets bagerste Del ere
smalere ved deres Udspring; paa Midten ere de 0,013""
tykke, og Enderne ere indtil 0.040"" brede. De saaledes
beskrevne 5 Kalkstykker ere yderst fine, og kunne
vanske-ligen opdages med det blotte Øje. Naar de ere i Situs,
danne de en femkantet Ring, idet de bagerste, fornemmelig
de længste Stave, naa saa langt til hverandre, at Ringen
derved afsluttes. Kalkstavene ligge ikke paa hinanden,
saaledes som Tilfældet er hos Elpidia og Irpa; men deres
Ender ere bundne sammen med Bindevæv, ligesom hele
Kalkringen ligger fæstet i den Bindevævshud, der danner
Svælgsinus. Kalkringen ligger en god Del foran
Vandkar-ringen; og Midtpartiet af ethvert af dens Stykker findes
just der, hvor de 5 Hovedstammer dele sig for at afgive
Grene til Tentaklerne, Tab. I, fig. 9, o, a. Paa
Kalkringens Stave fæster sig dels Muskelbaand, dels
ßindevævs-traade, der udgaa fra Svælget og fra Mundskiven. Til
nogen synderlig Støtte for Noget kan visselig ikke
Kalkringen tjene, da den er saa yderst fint bygget.
Vandkarsystemet.
Ringkanalen er dækket af den Bindevævsmembran,
der danner Svælgsinus. Denne Membran, der er temmelig
tyk, er fastvoxet til den bagerste Del af Ringkanalens ind-
sulated Nematoids; we failed, however, to detect any organic
disturbance, saving traces of muscular atrophy where the
Nematoids lav embedded.
Calcareous Skeleton.
The calcareous ring is imperfectly developed, indeed
almost rudimentary : true, it presents considerable
resemblance to the calcareous ring in Elpidia and Irpa, but
is of far more slender dimensions, and less compactly put
together. It consists of’5 calcareous segments, PI. III. fig. 27.
corresponding to the radial plates in other Holothurians.
Each, of these segments, measuring about 1.5"" in length, has
an almost quadrate central section, fig. 28, a, 0.068""
broad, and not quite so deep. This central section is, as
it were, bipartite, the anterior part being the narrower.
Affixed to the anterior part are 6 calcareous rods, two of
which protend obliquely forwards in the direction of the
oesophagus, with a slightly claviform extremity, fig. 28, b. b;
the remaining 4, each of which branches out a little above
the point of ofigin, with two ramifications, fig. 28. r, c, and
protends posteriorly upwards, apparently protending along the
tentacular vessels. To the posterior part of the central
section are affixed on either side 4 long calcareous rods,
fig. 28,d,d,d,d, radiating, as it were, to the sides, the longest
of which protends somewhat obliquely towards the extremity
of the corresponding rod on the calcareous segment next
adjacent, fig. 27, a. a. These rods have petaloid extremities,
furuished with apertures and incisions, fig. 28. The rods
springing from the posterior part of the central section, are
slenderest at their origin; in the middle, they measure
0.013"" in thickness, having a breadth of 0.040"" at the
extremities. The 5 calcareous segments described above are
exceedingly minute, and can with difficulty be discerned with
the naked eye. When in situ, they present the appearance
of a pentagonal ring, the posterior rods, and in particular
the longest of them approximating sufficiently to close the
ring. The calcareous rods do not lie one above the other,
as in Elpidia and Irpa. but their extremities are webbed
together by connective tissue, and the ring itself lies wholly
embedded in the membrane of connective tissue forming the
pharyngeal sinus. The calcareous ring is placed
considerably in advance of the water-vascular ring; and the central
section of each of its segments is located exactly where the
5 principal stems ramify to the tentacles, PI I. fig. 9, a. a.
The rods of the calcareous ring are pinnated with
muscular bands and filaments of connective tissue, proceeding from
the gullet and from the buccal disk. From the extreme
fragility of its structure, the calcareous ring can hardly
be of much importance as a means of strengthening any
part of the organism.
Aquiferous System.
The annular canal is enveloped by the membrane of
connective tissue constituting the pharyngeal sinus. This
membrane, which is rather compact, is connate with the posterior
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