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19
Endelig skulle vi omtale Stenkanalen, der ender blindt
udad, hvor den efter at have perforeret Muskelhuden fæster
sig til Coriums indre Flade. Stenkanalen er ifølge Théels
Iagttagelser fri for Kalk og uden Madreporplade; kun en
Gang mener han at have seet et lille Legeme af 0.02""
Diameter, og som forekom ham at bestaa af bueformige
Spikler, der havde sit Sæde paa Stenkanalens øverste Del.
Vi kunne supplere dette derhen, at paa den yderste
(øverste) Ende af Stenkanalen, der hvor den er fastvoxet til
Huden, findes smaa bueformige Kalkspikler, der dels ligge
enkeltvis og ligesom omgive Kanalen, dels ere de noget
større, ligge samlede og danne Fletninger, der kunne ansees
for en rudimentær Madreporplade, Fig. 16, a, 16’; hvorvidt
der i Kalkfletningernes Masker ere Aabninger eller Spalter,
der føre ind til Kanalen, kunne vi ikke afgjøre; thi
Fletningerne ligge egentlig i det Bindevæv, hvorved Kanalen
er fæstet til Huden, Fig. 16, a.
Slægten Kolga maa med Hensyn til den Plads, den
indtager i Holothuridernes Række, stilles meget lavt.’ Den
er i enkelte Henseender bleven staaende paa Larvestadiet,
— saaledes aabner Stenkanalen sig udad med en Pore,
hvorved Vandkarsystemet, ligesom hos Larven, staar i
umiddelbar Forbindelse med Søvandet, noget der ikke tidligere
har været paavist hos nogen Holothuride. Ser man saa
hen til den øvrige Organisation, — saa finde vi: at
Vandkarsystemet er temmelig ufuldkomment, har kun to
Længdekar; at Hudens Bindevæv er gjennemgaaende hyalint, har
ikke kunnet hæve sig op til en fibrillær Form; at Kalken,
som findes i den, har Spikelformen. og kun paa et enkelt
Sted, Mundskiven, og det endog meget sparsomt, antager
en mere sammensat Skikkelse, nemlig gjennemborede Skiver.
Det indre Skelet, som bestaar af 5 yderst smaa
Kalkstykker med fine udløbende Spikler, kan betragtes som
rudi-mentaft-t, tjener ikke til Støtte eller Fæstepunkt for
Længdemusklerne; thi dertil er det altfor spædt, og minder om
Kalkstaphelierne hos Echinodermlarverne. Tarmkanalen er
ikke forsynet med de Afsondringsorganer, som man har
kaldt Lunger. Nervesystemet kunde i første Øieblik synes
at staa temmelig høit paa Grund af den Masse
Sandse-organer (Høreblærer), som findes paa de to
Ainbulacral-nerver; men erindrer man, at det netop er hos en anden
lavtstaaende Holothuride (Synapta), og hos enkelte
Echino-dermlarver. at lignende Organer ere fundne, saa forekommer
det os. at denne Særegenhed ved Nervesystemet ikke kan
give Anledning til at sætte Slægten Kolga høiere op i
Rangen. Naar man ser hen til den overordentlig store
Mængde af det nævnte Sandseorgan, som findes langs
Am-bulacralhjernen, saa kunde man fristes til at spørge, om
disse Organer virkelig staa i Hørelsens Tjeneste; thi det
er ikke godt at forstaa, at et saa lavtstaaende Dyr skulde
være saa rigt udstyret for Sandsningens Vedkommende.
In conclusion, we will -briefly notice the sand-canal,
which, exteriorly, has a cæcal termination, at the point
where, after piercing the muscular layer, it is webbed to
the inner surface of the corium. According to Dr. Théel,
the sand-canal exhibits no trace of calcareous deposit, nor
is it furnished with a madreporic body; once only does
he believe to have detected a minute corpuscle, 0.02"" in
diameter, composed apparently of arcuate spiculæ, near the
upper extremity of the stem. This observation we are
enabled to supplement, in so far as the superior
termination of the sand-canal, where it is connate with the skin,
exhibits numbers of minute, arcuate calcareous spiculæ,
some disposed singly, and. as it were, circumscribing the
stem, the others, somewhat larger in size, being laced
together, forming a spiniferous network, which may be
regarded as a rudimentary madreporic body, fig. 16, a, 16’;
but whether the meshes of this calcareous network assume
the form of more or less circular openings, or of fissures,
we are unable to determine, the network lying embedded
in the layer of connective tissue that webs the stem to the
integument, fig. 16. a.
As regards its position in the scale of organic
development, the genus Kolga ranks very low among the
Holothuriidæ. In several respects indeed it has not emerged
from the larval stage: thus, for instance, the sand-canal
opens exteriorly through a pore, with which the
aquiferous system communicates directly with the searwater. a
characteristic feature not previously observed in any
Holo-thurian. Glancing further at the anatomical structure of
the animal, we find the aquiferous system, which is rather
simple in development, furnished with two longitudinal
vessels; the connective tissue of the integument, too. is
hyaline throughout, exhibiting nowhere traces of having
attained a fibrillous character ; moreover, the calcareous
deposit it contains is of the spicular form ; on one part only
of the organism — the oral disk, and even there to a
limited extent, does it assume a more complex structure,
occurring as perforated laiuinæ. The inner skeleton, which
consists of 5 exceedingly minute calcareous plates, with
slender protending spiculæ. may be regarded as
rudimentary. since it does not serve to strengthen the longitudinal
muscles, or to furnish them with a point of attachment:
indeed it is far too fragile, bearing considerable resemblance
to the calcareous stapheliæ in the larval forms of
Echi-nodermata. The intestinal canal is not provided with the
secretory organs which have been termed respiratory trees. At
the first glance the nervous system does indeed seem to be
highly developed, by reason of the large numbers of
sen-soria (auditory vesicles) on the two ambulacral nerves; but
if we call to mind that similar organs occur in another
low-organized Holothurian (Synapta), and in a few larval
forms of Echinodermata. this peculiar feature in the
nervous system is, we conceive, quite inadequate as a reason
for placing the genus Kolga higher up in the scale of
structural development; nay the immense number of
these sensoria is in itself suspicious; it would seem to
warrant our doubting their alleged subservience to the
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