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40
Nervesystemet.
Nerveringen omgiver den øverste Del af Svælget, er
uregelmæssig rund. temmelig smal og er indésluttet i en
Skede (Nervekarret). Den har en temmelig stærk gul
Farve, og har et’ ydre Cellelag og et indre Fiberlag.
For-udeu en Mængde mindre Grene, som afgives til Spiserøret,
Tentaklerne og Mundskiven, udgaa 5 Hovedstammer
(Ra-(lialstammer) fra den. Disse gaa ud igjennem det lille Hul,
ilsom lindes paa hvert af Kalkringens Radialstykker, og naar
de komme paa den ydre Flade af dem, løbe de over
Radial-musklen hen til Huden, hvor de fortsætte sit Løb imellem
denne og Ringmusklerne til omtrent Midten af Kroppen,
hvor de kun dækkes af Længdemusklerne, idet, som tidligere
bemærket. Ringmusklerne her ophøre noget indenfor
Længdemusklens Rand uden at gaa over Radialnerveu. Længere
bag paa Kroppen indtræder atter det tidligere Forhold, og
nu er Radialnerveu dækket af baade Ring- og
Længdemuskelen lige til Analaabningen. Der hvor -Radialnerven
træder ind i Kalkringens Radialstykke. lindes paa hver Side
af den en rund klar Blære, der dannes af en temmelig fast,
gjennemsigtig Membran, hvis Indhold var en klar Vædske
uden Otolither. Disse Blærer svare til de saakaldte
Høreorganer. der findes i større og mindre Mængde hos
Elpidi-Äerne, og som baade Dr. Théel og vi tidligere have
paa-vist, — kun er Forskjellen den. at de hos Acanthotrochus
ingen Otolither have. hvilket, ifølge Théels Angivelser,
ogsaa skal være Tilfældet hos den af ham beskrevne
Trocho-derma elegans. Er dette et mere primitivt Stadium af
Høreorganet, eller skulde det tyde hen paa. at disse Blærer
ingenlunde ere specielle Sandseorganer?
Radialnerverne ere indesluttede i et forholdsvis vidt
Kar, der paa Nervens indre Flade er sammenvoxet med
denne. Tab. V. Fig. 9. g, medens Karret paa den ydre
Side er aabent. Fig. 9. h. Dette Forhold er ganske
modsat af det Dr. Teuscher angiver at være Tilfældet
hosCri-noiderne, Echiniderne og Holothuriderne, hvor Radialnerven
med sin ydre, brede Flade er sammenvoxet med
Karvæggen. ’ Om Karret er forsynet med Endothelceller skulle vi
ikke med Sikkerhed kunne .afgjore; thi det var os ikke
muligt, selv under meget stærk Forstørrelse, at opdage
saadanne. Selve Nervestammen bestod af et lysere, bredere
Lag, Fig. 9, i, og et mørkt smalere. Fig. 9, k, der vendte
indad og var sammensmeltet med Karvæggen. Nerven
bestod af et peripherisk Cellelag og et centralt Fiberlag. Fra
Radialnérverne udgik langs hele Løbet en Mamgde Grene
til Musklerne og Huden.’
Generationsorganerne.
De faa Exemplarer (4). vi have havt til vore
Undersøgelser, vare samtlige Hunner. Kjonsorganet hos Hunnen
Nervous System.
The nervous ring surrounds the upper portion of
the oesophagus; it has a somewhat irregular circular form, is
rather narrow, and is enclosed in a membranous sheath (the
nervous vessel). It has a rather deej» yellow colour, and
is furnished with an outer cellular layer, and an inner
fibrous layer. Exclusive of numerous smaller ramifications
passing to the oesophagus, the tentacles, and the oral disk. 5
large stems (the radial stems) proceed from the outer
margin of the ring. These stems project through the small
aperture on each of the radial segments composing the
calcareous ring; and after reaching their outer surface, they
extend across the radial muscle to the integument, from
whence they continue their course between the latter and
the annular muscles nearly to the middle of the body,
where they are covered by the longitudinal muscles alone,
the annular muscles, as before stated, terminating here a
little within the margin of the longitudinal muscle,
without crossing the radial nerve. Farther down the body, the
radial nerves are covered both by the annular and the
longitudinal muscles till they reache the anal opening.
. Where the radial nerve pierces the radial segment of the
calcareous ring, on either side of tile nervous stem, is seen a round,
bright vesicle, consisting of a firm, transparent membrane;
they contained each a limpid fluid, without Otoliths. These
vesicles correspond to the so-called auditory organs that
occur — more or less numerous — in the Elpididæ. and
to which attention has been previously called both by Dr.
Théel and by ourselves. — with this difference, however,
that in Acanthotrochus they have no Otoliths, which,
according to Df\ Théel’s description of Trochoderma elegans, is
also the case with that species. Does this characteristic
feature represent an earlier stage in the development of
the auditory organ, or are we rather to infer, that these
vesicles have no sensorial function whatever?
The radial nerves are enclosed in a comparatively
capacious vessel, which, on the inner surface of the nerve,
is connate with the latter, Pl. V, fig. 9, g, and open on
the outer surface, fig. 9, h. This feature is exactly the
reverse of that stated by Dr. Teuscher as characteristic of
the Oritioidea, Echinoidea, and Holothuroidea, in which the#
outer broad surface of the radial nerve is connate with the
wall of the vessel. AVhether the vessel be furnished with
endothelial cells, is a question to which we can give no
conclusive answer, seeing it was impossible to detect, any,
even with the aid of a powerful magnifier. The nervous
stem consisted of a light, broad layer, fig. 9, i, and of a
dark, narrow one, fig. 9. k; the latter was directed
inwards, and coalesced with the wall of the vessel. The nerve
was composed of a peripheral cellular layer and a central
fibrous layer. From the radial nerves — throughout their
entire length — numerous offshoots proceeded to the
muscles and the skin.
Generative Organs.
The few specimens (4) we have had the opportunity
of examining were all females. The generative organ in
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