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92
Ihvorvel de nu beskrevne Organer i høi Grad afvige
fra de hidtil kjendte Pedicellarier, have vi dog benævnet
dem saaledes, fordi de, efter vor Formening, nærmest maa
henføres dertil. De konstatere paa det Evidenteste
Professor Agassiz’s Iagttagelser, at Pedicellarier ere kun en
yderligere Udvikling af Pigge; thi ligesom Agassiz har
forfulgt Piggens Udvikling til Pedicellarie, saaledes kan man
hos Bathybiaster meget let finde de for denne Udvikling
nødvendige Overgange.
Randpladerne, der ere stillede lige overfor hinanden,
ere 5.5""" brede og 2mm høie paa den nærmest Skiven
til-grændsende Del af Armen paa det største Exemplar; 4.5™"’
brede og 2mm høie paa Armens Midte. Deres Siderande
ere forsynede med en Rad tætstaaende, runde Papiller og
deres Flader ere overalt bedækkede med fine, næsten flade,
taglagte Kalkskjæl, Fig. 1. 2.
De dorsale Randplader have en næsten
perpendikulær Stilling og gaa ikke ind paa Ryggen af Armene;
henimod deres ydre og øvre Rand ere de forsynede med en
flad Torn, Fig. 2, a.
De ventrale Randplader, der staa lige overfor de
dorsale, have flade Torne; de inderste Plader (nærmest
Skiven) bære 4, der staa i en Række og ere lige lange;
længere ud paa Armen er der 3 og saa 2, indtil endelig de
ydre Plader have kun 1 Torn. Ligesom Tornene aftage
i Antal, saaledes 7aftage de ogsaa i Størrelse, Fig. 2, b.
Hudskelettet paa Rygfladen er paa hele Skiven
sammensat af temmelig smaa, mere eller mindre runde Plader,
der ere taglagte, og fra Skiven gaar et bredt Belte af
lignende Plader langs Armenes Midtparti lige ud til
Spidsen, aftagende efterhaanden i Bredde. Paa begge Sider af
dette Belte hen til Randpladerne dannes Skelettet af smaa,
stjerneformige Plader, der ere taglagte; men paa Grund af
Udløberne fremkomme et Slags tæt Kalknet med yderst
smaa Masker, hvori i Regelen er en Tentakelpore, Fig. 12.
Disse stjerneformige Plader ere paa deres indre Flade kun
lidet hvælvede, paa deres ydre Flade, Fig. 11. have de en
ophøiet, aflang Flade, der bærer Paxillen. Hverken paa
Skiven eller paa Midten af Armene findes Tentakelporer.
Bugfladens Hudskelet dannes af temmelig store,
aflange, taglagte Kalkplader, der i Inierbrachialrummene ere
placerede i regelmæssige Rækker; den udvendige Flade af
Pladerne har mange smaa, runde Knuder, der bære de
tidligere omtalte siddende Pedicellarier.
Ambulacralpladerne udmærke sig ved sine
overordentlig brede, bladformige Sideprocesser, paa hvis indvendige
Flades Midte findes en fremi agende Kam, hvortil den
temmelig lange, smale, listeformige Ambulacralstøtte (soutien
ambulacraire) er fæstet. Sideprocessens ydre Flade har en
større og en mindre Artikulationsflade, der støder til de to
tilsvarende Adambulacralplader.
Although the organs just described, differ in great
degree from the pedicellariæ previously known, we have
still designated them thus, because, in our opinion, they
are nearest allied to these. They confirm, most
conclusively, Professor Agassiz’s observations, that pedicellariæ are
only an extended developement of spines, because, just as
Agassiz has followed the development of spines into
pedi-cellariæ, can we, in Bathybiaster, very easily, find the
necessary transition stages for this development.
The marginal plates are placed right opposite to each
other, and in the largest specimen, they are 5.5""" broad,
and 2mm thick, at the part of the ray adjoining the disk,
and 4.5""" broad, and 2mm thick, in the middle of the ray.
Their lateral margins are • furnished with a series of close
set papillæ, and their surfaces are, everywhere, covered with
minute, flat, imbricate scales (fig. 1. 2).
The dorso-marginal plates are situated in a nearly
vertical position, and do not extend into the dorsal surface
of the rays. Towards their superior and exterior margins,
they are furnished with a flat aculea (fig. 2, a).
The ventro-marginal plates are placed right opposite
the dorso-marginal plates, and have flat aculeæ. The
inner plates (nearest the disk) carry four aculeæ of equal
length, arranged in a series. Further out upon the ray,
there are three aculeæ, and still further out, two, until,
finally, the outer plates have only one aculea. Just as the
aculeæ diminish in number, so do they, also, diminish in
size (fig. 2, b).
The dermal skeleton of the abactinal surface, is, upon
the entire disk, composed of rather small, more or less
round, plates, which lie imbricate. From the disk, a broad
belt of similar plates proceeds, extending along the mesial
line of the rays, right up to the tip, but gradually
diminishing in size. On each side of the belt, towards the
marginal plates, the skeleton is formed of small asteriated
plates, which are imbricate, but by means of the
prolongations, produce a kind of compact calcareous reticulation
with extremely fine meshes, in which a tentacular pore is
usually seen (fig. 12). These asteriated plates, are only
slightly convexed on their interior surface, but their
exterior surface is arcuate, and oblong, and it carries a paxilla
(fig. 11). Neither upon the disk nor upon the middle of
the rays are tentacular pores seen.
The actinal dermal skeleton, is formed, of rather large,
oblong, imbricate calcareous plates, placed in regular series
in the interbrachial spaces. The exterior surface of the
plates, has many small round knobs, which carry the sessile
pedicellariæ previously spoken of.
The ambulacral plates are distinguished, by their
remarkably broad leaf-formed lateral processes, in the middle
of whose interior surfaces, there occurs a prominent ridge,
to which the rather long narrow fillet-formed ambulacra!
supports (soutien ambulacraire) are secured. The exterior
surface of the lateral processes, has a large and a small
articulatory surface, which butt with the corresponding
ad-ambulacral plates.
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