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54
strømmet Søvand, iiien maa have faaet det paa endosmotisk
Vei, noget der jo er meget almindeligt for organiske
Membraner. Kommer nu hertil, at de forgrenede Rør hos
Trochostoma ikke ere forsynede med særegne Blodkar, formene
vi. at de mangle alle Betingelser for at kunne faa Navn
af Lunger.
Det forekommer os. at de foreliggende Kjendsgj era
inger paa det Bestemteste maa fraskrive disse Organer al
Ret til at ansees for- at staa i Aandedrættets Tjeneste, men
at de meget mere maa anses som Afsondringsorganer. der
tilhøre Tarmen, og forsaavidt formene vi for Trochostomas
Vedkommende at have bevist Rigtigheden af Johannes
Mül-lers og Gegeubauers Antagelse, den nemlig, at de saakaldte
Lunger ere analoge Organer til de interradiale Blindrør
hos Asteriderne. Men forholder det sig saa hos Slægten
Trochostoma, saa er der liden Grund til at antage, at
Forholdet er anderledes for de selvsamme Organer hos de
øvrige Slægter af Lunge-Holothuridernes store Gruppe. Vort
Dyr staar unægtelig paa et temmelig lavt Trin i Familien
og tør derfor ogsaa i phylogenetisk Henseende have sin
Interesse.
Det indre Skelet.
Kalkringen dannes af 10 Stykker. 5 radiale og 5
interradiale, hvilke ere sammenbundne med en stærk
Binde-vævsmasse, Tab. VII, Fig. 5. Hos unge Dyr er denne
tommelig svag, saa at Stykkerne med Lethed kunne skilles
fra hverandre, imedens Forbindelsen hos udvoxne Dyr er
saa stærk, at den kun kan hæves ved Kniven eller ved
Hjælp af en koncentreret Kalilud.
Radialstykkerne ere 5"™ lange. 3™" brede paa Midten,
og ere ikke ganske symetriske. forsaavidt det ene kan være
lidt smalere og lidt skjævere end det andet, Tab. VII. Fig.
5, a, a, a. Hvert Radialstykke har en bredere Del, som
danner det egentlige Legeme (Corpus). Fig. 5, b, 4), 6, b.
og en Forlængelse (Processus). Fig. 5, a, a, 6, a.
Legemet har en udvendig og en indvendig Flade, to Sideflader
og en øverste Rand. Den udvendige Flade er lidt kon vex
mod Siderne og forsynet med 3 fremspringende Kamme
(Cristæ); de indtage hele Fladens Længde og divergere
lidt nedad. Fig. 5, c. Den midterste Kam er den mest
fremragende; Sidekammene udgjøre egentlig Siderandeue.
og blive først tydelig fremspringende, idet den ene Rand
føies til en anden fra det tilsvarende Radialstykke.
Imellem disse tre Kamme ere to temmelig dybe Furer,
hvoraf den ene — den udvendige — lukkes foroven
og danner her’ den skeformige Grube, hvori insererer sig
den fælles Tendo for to Længdemuskler. Fig. 5, d, d. I
den indvendige Fure. der altsaa Andes mellem Midtkammen
og den venstre (indvendige) Kam. ligger en Ampulla. Fig.
5. e. Den venstre Kam rager lidt over den øvre Rand.
saa at denne derved faar et halvmaaneformigt Indsnit.
Fig. 6, c. Den indvendige Flade er lidt konkav mod Si-
The tubes with their vesicles cannot therefore derive tlieir
contents from an influx of sea-water; the presence of the
fluid must be traced to endosmotic action, which indeed
is very frequent in organic membranes. Moreover, the
ramose tubes in Trochostoma are not even provided with
special blood-vessels, and hence, we think, they fail to
exhibit any one of the features that would entitle them to
the name of respiratory organs.
The facts we have adduced furnish, in our opinion,
the strongest presumptive evidence that these organs are
nowise subservient to respiration, but should rather be
regarded as secretory organs proceeding from, and belonging to,
the intestine; and hence, so far at least as concerns the genus
Trochostoma. we believe to have substantiated the
correctness of Johannes Miiller’s and Gegenbauer’s assumption, viz..
that these "lungs" are organs analogous to the interradial
cæca-like tubes in the Asteridæ. But if this be the case
with Trochostoma, the function of the selfsame organs in
other, genera belouging to the great group of lung-respiring
Holothurians must surely be identical. The animal here
described ranks low in the family Molpadidæ, and may
therefore, phylo-genetically. prove an. interesting acquisition.
The Caloareous Skeleton.
The calcareous ring is composed of 10 segments — 5
radial and 5 iuterradial. webbed together byja oompact mass
of connective tissue, Pl. VII. fig. 5. In young examples,
the tissue is rather fragile, and the segments readily admit
of being parted, but in full-grown individuals they adhere
so tenaciously that a knife, or a concentrated solution of
potash, is needed to dissolve the connexion.
The radial segments’are 5""" long. 3"" broad in the
middle, and not quite symmetrical, some being a trifle narrower
and more oblique than others. Pl. VII. fig. 5, a, a, a.
Each of the radial segments has a broad part. which
constitutes the body (corpus), fig. 5, b, b. G, b, and an
elongation, or process, fig. 5, a, a, 6, a. The body has an outer
and an inner surface, two lateral surfaces, and an upper
margin. The outer surface — slightly convex towards the
sides — is furnished with 3 projecting combs (crista?), which
occupy the whole length of the surface, diverging slightly
downwards, fig. 5. c. The middle comb projects most; the
lateral combs constitute, strictly, the lateral margins, and do
not assume a projecting appearance till one margin unites
with another from tlie corresponding radial segment. Between
these three combs extend two rather deep grooves, one of
which — the outer groove — is closed above, forming a
spoon-shaped socket, from which springs the tendon
common to two of the longitudinal muscles, fig. 5. d, d. In the
inner groove, extending accordingly between the middle and
the left (the inner) combs, is seen an ampulla, fig. 5. e.
The left comb projects slightly above the upper margin,
producing therein a lunate incision, fig. G. c. The -inner
surface is slightly concave towards the sides, and ’ exhibits
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