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52
sidste nedstigende Slynge, uden at være bunden til den, og
hverken den ene eller den anden staar i nogen Forbindelse
. med Karsystemet.
Det har været almindelig antaget, at disse forgrenede
Rør tjene som Respirationsorganer, idet de skulle optage
Søvandet fra Kloaken, og efter at have afgivet det fornødne
Surstof til Blodet, skulde’ det igjen udstødes, tilsat med en
Del af de for Blodet ubrugelige Stoffe.
Hos en hel Del Holothurider foregaar ogsaa en
rhyt-misk Udvidning og Sammentrækning af Kloåkaabuirigen,
hvorved Søvandet inddrages og udstødes; men om dette
jages op igjennem Rørene og fylder de mangfoldige Blærer,
der da skulde sammentrække sig for atter at støde Vandet
ud, eller med andre Ord, om der virkelig i de nævnte Rør
og Blærer foregaar en Diastole og Systole, saaledes som
Tilfældet er med Lunger i Almindelighed, det tør være
Tvivl underkastet. En saadan Tvivl har ogsaa til
forskjellige Tider været reist; saaledes er Johannes Mttller den
første, der har ytret den Formening, at disse saakaldte
Lunger neppe staa i Respirationens Tjeneste, da det
forekom ham besynderligt, at kun den ene Stamme havde
Blodkar, imedens den anden var uden Blodkarforbindelse
med Tarmen. Han er tilbøielig til at antage dem for
Appendices til Fordøielseskanalen, og sammenligner dem
med Analblinderørene hos Asteriderne.
Gegenbauer1 deler vistnok den samme - Mening og
henfører dem til Tarmkanalens Tilhængsorganer. idet han
ytrer: •’Omendskjøndt disse saakaldte Lunger — indre
Aandedrætsorganer — med Hensyn til deres Funktion ere
forskjellige fra de interradiale Blindrør paa Søstjernetarmen,
saa komme de dog disse nær i morphologisk Henseende og
synes at være en videre Udvikling af de hos Asteriderne
forekommende meget simple Rør". Men hverken Johannes
Mdller eller Gegenbauer har, saa forekommer det os, kunnet
levere noget fuldgyldigt Bevis, støttet paa rene Iagttagelser,
for deres Mening, hvorfor de ogsaa opfordre Forskere til
at skjænke disse Organer deres fulde Opmærksomhed.
Vi have paavist, at hos Trochostoma, hvor disse
antagne Lungeapparater ere meget udviklede, udspringe de
fra selve Tarmen uden nogen Karforbindelse med denne.
Heldigvis have ri havt flere Exemplarer i forskjellige
Udviklingsstadier at raade over, saa at Observationerne derved
have vundet i Sikkerhed.
Hos et 10"" langt Individ, hvor intet Spor saaes til
Generationsorganerne, fandt vi Rørene ikke meget
udviklede; det høir-e dannede ved sit brede Udspring en
tragt-formig Forlængelse af Tarmvæggen, hvilken indtog omtrent
en Trediedel af Dyrets Længde, og var aldeles opfyldt af
det samme lerede Indhold, som den fuldproppede Tarm,
Tab. VII. Fig. 11, a. Ved den øverste spidse Ende af
Tragten blev Røret tyndt og næsten- vandklart; men snart
1 Gegenbauer. Grundriss der vergleichenden Anatomie. 2te
AuH. 1878, pag. 228.
tube, or tree, is placed close to the last descending
convolution of the intestine, without however being webbed to it,
and neither the one nor the other have any connexion
whatever with the vascular system.
These ramose tubes have generally been regarded as
performing the office of respiratory organs, the water being
sucked up through them from the cloacum, and then, after
it has . given off the necessary amount of oxygen to the
blood, ejected, with some admixture of substances eliminated
from the blood.
In many Holothurians there is a rhythmic expansion
and contraction of the cloacal opening, whereby the
water is sucked in and ejected; but whether it be forced
up through the tubes and fill the numerous vesicles, which
in that case would, as in other inspiratory organs, contract
and expand with a regular alternate stroke — systole,
diastole — to expel the aquiferous fluid, is doubtful. Indeed this
is a question which has been frequently raised. Johannes
Müller was the first to state that, in his opinion, these
-lungs" could hardly perform the office of respiration; it.
struck liim as strange, that one only of the respiratory
tubes should be furnished with blood-vessels and the other
have no circulatory connexion whatever with the intestine.
He would regard them rather as appendices to the digestive
canal, and compares them to the cæca-like anal tubes in
the Asteridæ.
Gegenbauer1 shares this view, regarding them as mere
appendages of the intestinal canal. He expresses himself
as follows:— "These ’lungs.’ as they are termed —
internal respiratory organs — do indeed, as to their function,
differ from the cæca-like interradial tubes in starfishes, but
morphologically they bear considerable resemblance to those
organs, and would seem to be a further development of
the very simple tubes in the Asteridæ." But neither Müller
nor Gegenbauer have, we think, furnished satisfactory proof,
from autoptical observations, of the soundness of their
hypothesis; indeed, they both call on naturalists to give these
organs a full share of attention.
Now. we have shown that this respiratory apparatus
originates in Trochostoma. which has it highly developed,
on the intestine itself, without however having any
vascular connexion with that organ. Fortunately, we have had
before us several specimens, representing different stages of
growth, which has given a more conclusive character to
our results. •
An example, 10"" in length, in which no trace
of generative organs could be detected, had the tubes but
slightly developed; the right tube formed at its origin
a funnel-shaped continuation of the intestinal wall,
occupying nearly a tliird of the length of the animal, and was
stuffed full of the same clayey substance that distended
the intestine, Pl. VII, fig. 11, a. At the superior
acuminate extremity of the funnel, the tube became thin
1 Gepenbauer. Grundriss der vcrjrleichenden Anatomie. 2te
Aufl. 1*7H, pag. 22K
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