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27
Diastopora maeandrina, Wood.
Bowerbanlåa arctica, Rusk.
Biiskia nitens. Alder.
Disse udgjør omtrent 14 pct. af samtlige arter i
fortegnelsen. Størsteparten af de ovenfor anførte arter er
heller ikke observeret ved Spitsbergen eller i Karahavet.
Af de 7 arktiske former, som forekommer ved Queen
Charlotte Islands men ikke ved britiske kyster er den kun
én nemlig Cellaria articulata, som endnu ikke er indlemmet
i vor fauna. De øvrige (5 (Flastra membranaco-tmncata,
Membranipora arctica, Myriozoum coarctation,
Rhamphosto-mella plicata, Cellepora incrassata, Retepora élongata) er
vel kjendte fra vor arktiske region.
Da jeg sommeren 1894 udenfor Nordkyn i Finmarken
tog op en Laminaria liyperborea, som fra grunden til
toppen (70 cm.) var tæt besat med Gemellaria lorieata i
yppig vekst, blev jeg slaaet over denne tydelige
tilkjendegivelse af livskraft. Paa min reise forleden vinter havde
jeg anledning til at skrabe nogoé i trange og strømsterke
sund i Finmarken, og det viste sig ogsaa der. at enkelte
arter som Gemellaria, Menipea, etc. havde en enestaaende
kraftig vekst. Studiet af polyzoerne bekræfter saaledes det
almindelige indtryk, at arktiske dyr i regelen er kraftige
og velfødde. Med andre ord, arktiske former viser over-,
legenhed i størrelse og udvikling i det hele taget fremfor
sin nære slegtninge blandt de boreale dyr. Dr. Pfeffer*)
udtaler ogsaa om polyzoerne: „Sie fobien nirgends vidlig,
sind aber in den Tropen und den grossen Tiefen sparsamer,
dagegen in den kälteren gomässigton Zonen am häufigsten
nächstdem in den polaren Zonen am hesten entwickelt".
Hvad kan grunden være hertil? Jeg tror, at polyzoernes
rige udvivling i de polire have hænger sammen med de
selvsamme haves store planktonrigdom. Ifølge sin bygning
og sit fastsiddende voksesæt er polyzoerne udelukkende
henvist til at leve af plankton eller af organiske rester,
som tindes suspenderet i vandet**). Heraf synes at frem-
*) Die niedere Tierwelt des antarktischen Ufergebietes.
**) Ved en enkelt anledning har jeg seet individerne i eu
polyzo-koloni foretage bevægelser, som jog opfattede som spisning.
Paa ruderne i et af akvarierne ved den biologiske station
havde nemlig fæstet sig kolonier af Membranipora membranacea,
ndentvil grundlagt af larver, som var indkomne med
ledningsvandet. .Teg kunde da tydeligt se, hvorledes polypiderne
uophørligt skjøv sin tentakelkrans sammenlagt i form af et
rør ud af mundingen, derpaa sprede kransen ud i tragtform
for saa efter en liden stunds forløb at trække den ind. Det
er muligt at dette ogsaa var en aandedrætsbevægelse, men at.
der paa den maade tillige skede en tilførsel af næring, synes
mig utvilsomt. Egentlig talt kan man neppe tænke sig nogen
anden maade at spise paa for disse dyr. I det samme
akvarium har jeg seet en sjøpølse (Cucumaria frondosa) foretage
tcntakelbcvægelser, som ganske sikkert havde med ernæringen
at, gjøre. Hos Cucumaria blev ikke hele tentakelkransen trukket
ind samtidig, men hver enkelt af hovedgrenene blev afvekslende
puttet ind i munden.
Diastopora maeandrina. Wood.
Bowerbanlåa arctica, Busk.
Buskia nitens, Alder.
These amount to about 14 per cent of the total
number of species in the list. The greater number of the
above-named species have not been observed in Spitsbergen
or the Kara Sea.
Of the 7 arctic forms that occur in Queen Charlotte
Islands, but not on the shores of Great Britain, there is
only one, namely Cellaria articulata, that has not yet been
incorporated in our fauna. The other 6 (Flustra
mem-branaeeo-truncata, Membranipora arctica, Myriozoum
coarctatum, Rhamphostomella plicata, Cellepora incrassata,
Retepora elongata) are well known from our arctic region.
In the summer of 1894, when, off Nordkyn in
Fin-mark, 1 drew up a Laminaria liyperborea that was covered
from top to bottom (70 cm.) with a luxuriant growth of
Gemellaria lorieata, I was struck with this clear evidence
of vital force. During my expedition last winter, I had
occasion to dredge a little in narrow channels in Finmark
where the current was strong, and it proved that there
too, certain species, such as Gemellaria, Jlenipea, etc.
were of an exceptionally strong growth. The study of
polyzoans thus strengthens the general impression that
arctic animals as a rule are strong and thriving. In other
words, arctic forms on the whole, exhibit a superiority as
to size and development, to their near relations among
the boreal animals. Dr. Pfeffer*) also says of polyzoans:
„Sie feillen nirgends vüllig, sind aber in den Tropen und
den grossen Tiefen sparsamer, dagegen in den kälteren
gemässigten Zonen am häufigsten nächstdem in den polaren
Zonen am besten entwickelt". What can be the reason
of this? I believe that the luxuriant development of the
Polyzoa in the polar sea is connected with the great
abundance of plankton in that sea. From their structure
and their fixed manner of growth, polyzoans are compelled
to live exclusively on plankton or organic remains that
are found suspended in the water**). From this it would
*) Die niedere Tiervelt des antarktischen Ufergebietes.
**) On one occasion I have seen the individuals in a colony of
Polyzoa going through movements which I took to be eating.
Colonies of Membranipora membranacea had fastened
themselves to the glass in one of the aquaria in the biological
station, without doubt growing upon larvæ that had come
in with the water-supply. I could distinctly see how the
polypides incessantly pushed out tlieir circlet of tentacles
folded together in the form of a tube, and then spread them
out in a funnel-shape, only to draw tliem in again in a little
while. It is possible that this was also a respiratory
movement, but I have no doubt whatever that in this way a
supply of nourishment was also taken in. Strictly speaking,
it is hardly possible to imagine any other way for these
animals to eat. In the same aquarium, I have also seen a
sea-cucumber (Cucumaria frondosa) making tentacular movements
which were certainly connected with feeding. In Cucumaria
the whole circlet of tentacles was not drawn in at once, but
each of the main branches was put into the mouth in turn.
4*
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