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64
Trochostoma (Molpadia)* boreale, M. Sars.
Syn. Molpadia eioUtcea, Studer?1
(Tab. X, Fig. T—11).
I vor tidligere Afhandling over Trochostoma
Thomsonii ytrede vi den Formening, at Sars’s Molpadia borealis
maatte blive at henføre til den af os opstillede Slægt
Trochostoma, da den efter Sars’s Beskrivelse ikke kunde være
nogen virkelig Molpadia. Fra Christiania Universitets
Samlinger have vi faaet udlaant Resterne af Sars’s
Original-exemplarer, nemlig endel Hud, noget af Tarmkanalen og
Kjønsorganerne. hvorved vi ere blevne satte istand til at
anstille Undersøgelser og Sammenligninger, der have bragt
os til fuldkommen Vished om, at Sars’s Art ikke er nogen
Molpadia, men en Trochostoma. Vi have ogsaa derved
faaet Anledning til dels at berigtige, dels at supplere Sars’s
Beskrivelse.
Med Hensyn til de ydre Karakterer skulle vi
bemærke, at den haleformige Forlængelse har rundt
Kloak-aabningen 5 Papiller (Tænder), lig dem hos Troch.
Thomsonii, hvilke have undgaaet hans Opmærksomhed.
Hudens histologiske Sammensætning er ikke forskjellig
fra den hos Tr. Thomsonii. derimod ere Kalklegemerne,
som ere leirede i Bindevævslaget, forskjellige, om end
Grundformen er den samme. De fremtræde under to
Hovedformer og i forskjellig Størrelse, nemlig de smaa. der ere
dels elliptiske, dels mere eller mindre runde. — og de
store, der ere mere sammensatte.
De elliptiske eller aflange. Fig. 7, a, 10. ligge tæt •
til hverandre og tildels paa hverandre, have en smuk
vinrød Farve og bestaa af temmelig regelmæssige concentriske
Ringe, der danne Lag. Fig. 10, imedens de mere runde
Kalklegemer, Eig. 11, have en gul Farve, ere mere ujævne,
bestaa ligeledes af Lag. men ikke saa regelmæssige, og ere
sammenhobede imellem de elliptiske. Saavel disse som de
runde danne ligesom et sammenhængende Lag, ovenpaa
hvilket de store Kalklegeiner hvile. Disse ere noget
forskjellige, alt eftersom de findes paa de forskjellige
Legemsdele, men den trearmede Grundtype gjenkjendes dog. Paa
begge Ender af Legemet ligge de temmelig tæt til
hverandre: Kalkpladerne ere her langstrakte med en Udløber
til hver Side, og fra Midten af den af Huller gjennembrudte
Plade hæver sig Skaftet, eller Kronen, der ved sin
Grunddel er treannet, men forøvrigt rundt, og udvider sig noget
i den frie Ende, som er forsynet med flere Takker. Fig. 8.
1 Dr. Th. Studer, Ueber Echinixlennon aus dem antarctischen
Meere. Monatsberichte der kun. preuss. Acadoinie der Wissenschaften
7.U Berlin. 1877, Pag. 4."»4.
Trochostoma (Molpadia) boreale, M. Sars.
Syn. Molpadia riolarea, Studer?1
(Pl. X. figs. 7-11).
In a previous Memoir treating of Trochostoma Thomsonii,
we expressed as our opinion that Sars’s Molpadia borealis
would have to be referred to the genus Trochostoma, since,
according to Sars’s description, it could not possibly be a
true Molpadia. From the Zoological Collection in the
University of Christiania we have obtained on loan all that
was left of Sars’s original specimens, viz. fragments of the
skin, of the intestinal canal, and of the generative organs,
which has enabled us to institute a series of comparative
observations; and the results obtained afford to our minds
conclusive proof that Professor Sars’s species is not a
Molpadia, but a Trochostoma. While conducting the
examination, we have also had an opportunity ot amending and
supplementing Sars’s description.
As regards the external charactex-s of the animal, we
must not fail to observe that the caudiform appendix is
furnished round the anal opening with 5 papillæ (teeth),
similar to those in Trochostoma Thomsonii, a feature not
detected by Sars.
The histological structure of the integument is the
same as in Tr. Thomsonii: the calcareous corpuscles,
however", embedded in the layer of connective tissue, though
the trifid form is fundamental in both, exhibit certain
differences. Varying as they do in size, we may divide
them into two groups, one comprising the small
corpuscles. some of which are elliptic and some more or less
globular, and the other the large corpuscles, distinguished
by a more complicate structure.
The elliptic-shaped, or oblong corpuscles, fig. 7, a, 10,
exhibit a close arrangement, lying one beside, nay
frequently upon, the other are of a beautiful vinous red, and
composed of comparatively concentric rings, forming layers,
fig. 10: the corpuscles approximating more a circular
form, fig. 11. are yellow in colour and not so smooth, but
also consist of layers — less regular however — and lie
crowded together between the elliptic-shaped corpuscles.
Both forms, the elliptic and the round, constitute each, as
it were, a continuous layer, upon which the large
corpuscles are disposed. The latter vary somewhat in form
according to the part of the body on which they occur : they
all. however, retain the trifid. three-armed type. At the
extremities of the body their arrangement is comparatively
close; here, the calcareous plates are elongate, with an
offshoot on either side: and from the middle of the perforate
plate, pierced with numerous holes, springs the shaft, or
corolla, which at its base is three-armed, but elsewhere
cylindric; at its free extremity, furnished with several
spikes, it slightly expands, fig. 8.
1 .Dr. Th. Studer. L’eber Echinodermen aus dem antarctischen
Meere. Monatsberichte der kön. preuss. Academie der W issenschaf’ten
zu Berlin, p. 4.">4: 1«77.
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