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34
egentlige Kanal taber sig, Fig. 7, c. Stenkanalen dannes
af en meget bred Bindevævsskede, hvori er afsat en Mængde
Kalk; selve Kanalen bestaar af et fastere Bindevæv, der
er uden Kalk.
Farven bleg rosenrød med brunlige Tentakelblade.
Ståt. 270. .
Med Hensyü til Oligotrochus vitreus, saa maa vi
til-staa, at vi i længere Tid have været i Tvivl oms hvorvidt
den kunde opretholdes som særegen Slægt; men af Mangel
paa tilstrækkeligt Sammenligningsmateriale maatte vi lade
Afgjørelsen staa hen til en gunstigere Tid. Denne kom,
idet vi fra Nordhavsexpeditionen blev forsynet med en stor
Mængde Exemplarer af Myriotrochus Rinkii og et
velkonserveret Exemplar af Huxley’s Myriotrochus (Chirodota)
brevis.
Vi tog nu fat paa at undersøge Oligotrochus vitreus,
og fandt, at de Kjendetegn, der skulde karakterisere
Slægten, faldt fuldstændig sammen med dem. der tilhøre
Myriotrochiis. Hjulene ere vistnok ikke stilkede; men paa de
Exemplarer, vi have undersøgt, ere de tilstede i ligesaa
stor Mængde som hos Myriotrochus. Ligesom Tilfældet er
hos denrie. at Bugtiaden kan stundom være ganske fri for
Hjul, og altid, naar de findes der, ere de yderst sparsomme,
— saaledes forholder det sig ogsaa hos Oligotrochus:
Har altsaa Sars undersøgt mest Bugfladens Hud, saa
lader det sig forklare, hvorledes det er gaaet til, at han
har fundet saa faa Hjul. Denne Omstændighed i Forening
med at Hjulene vare stilkløse, har motiveret Sars til dt
opstille en ny Slægt. Men, som vi have seet, har M.
brevis heller ikke stilkede Hjul, hvilket Sars dengang ikke
kjendte til. Selv vaklede han imellem at danne en ny
Slægt, eller at henføre den til Steenstrup’s Myriotrochiis;
men han bestemte sig til det Første. Yi have ikke fundet,
hverken, i de ydre eller i de anatortiisk-histologiske
Kjendetegn, Noget der kan adskille den fra Myriotrochus, og vi
ere saaledes nødsagede til at inddrage Slægten Oligottochus.
Hvad nu Arten angaar, saa falder den ganske
sammen med Myriotrochus brevis. At Sars dengang antog den
for at være forskjellig fra Rinkii, var jo i sin Orden, og
da han ikke har kjendt Huxlev’s Chirodota brevissaa faldt
det af sig selv; at han gav den et nyt Navn. Men efter
de Undersøgelser, vi have anstillet over Oligotroclius vitreus,
calcareous spicules give a rough surface, the canal itself
coalesces, fig. 7, c. The sand-canal is enclosed in an
exceedingly broad sheath of connective tissue, strengthened
by an abundance of calcareous deposit; the canal itself
consists of connective tissue, firm in texture but without
calcareous deposit.
Colour a pale rosy red; the tentacular pinnæ brownish.
Station 270.
We must confess we have long felt very doubtful as
to whether Oligotrochus vitreus would in the end be found
to constitute a separate genus; but the materials before us
being insufficient for pronouncing a decided opinion, we
deemed it best to defer our judgment till a more favourable
opportunity should enable us to institute conclusive
observations. Nor did we wait in vain; for on the return of
the North-Atlantic Expedition, numerous examples of
Myriotrochus Rinkii and a well-preserved specimen of Huxley’s
Myriotrochus (Chirodota) brerns were submitted to us for
examination.
We forthwith renewed our observations on
Oligotrochus vitreus, and were not surprised to find, that the
characters said to distinguish the genus do not in any respect
differ from those of Myriotrochus. True, the wheel-shaped
spicules are not pedunculate; but in the specimens we have
examined they are as numerous as in Myriotrochus. And,
as is the case with the latter, the ventral surface in
Oligotrochus has sometimes not a trace of these spicules,
which, when they do occur there, are always very sparingly
distributed.
Supposing, then, that- Sars confined his observations
chiefly to the integument of the ventral surface, the fact
of his having found so few wheel-shaped spicules is at
once accounted for. It was this paucity of spicules
in conjunction with their non-pedunculate character that
induced Sars to establish a new genus. But neither are, as
we have seen, the wheel-shaped spicules in M. brevis
pedunculate, a feature of which Sars was at that time ignorant.
Nay, he himself wavered between establishing a new
species or referring the animal to Steenstrup’s Myriotrochus;
but the balance dipped in favour of the former alternative.
Neither in the exterior nor in the anatomical-histological
characters have we lighted on any genericallv distinctive
feature which it does not share with Myriotrochus; and
hence the genus Oligotrochus should, we opine, be no longer
retained.
And as regards the species, it agrees in every respect
with Myriotrochus brevis. In deeming it specifically distinct
from Rinkii, Sars is found to have been quite correct, and
as Huxley’s Chirodota brens was unknown to liim, it was
but natural lie should give it a new name. But, according
to our observations Oligotrochus vitreus and Myriotrochus
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