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78
for den indre, halvkugleformige Fremstaaenhed, der tjener
til Støtte for Ambulacralpladens Tverproces, udspringe to
temmelig lange Kalkpigge, der tage deres Retning indad
mod Bugfuren, hvis halve Bredde de indtage, Fig. 2, a. 5.
13, d. Samtlige disse Pigge ere forsynede med konkave
Ledflader, der svare til de smaa, runde Forhøininger paa
Adambulacralpladens Midtparti. Foruden disse 3
artikulerende Pigge findes paa en stor Del af de indre
Adam-bulacralplader endnu en 4de Pig, der sidder omtrent midt
imellem de 2 store Randpigge; den er temmelig kort og
har en bred Basis. Det første Par Adambulacralplader
smelte sammen med de tilsvarende fra hver tilgrændsende
Arm og danne derved de 5 Mundvinkelplader. Disse ere
tykke, stærke, aflange, med en Søm efter Midten og
forsynede med 6 lange (3 paa hver Side) tilspidsede,
articule-rende Kalkpigge (Tænder), |der vende ind mod
Mundaab-ningen, Fig. 2.
Paa Bunden af den store Ryghule, i et
Interbrachial-ruin paa Grunden af en Arm, sees Madreporpladen, Fig.
7, i, der er ægdannet med den bredere Del indad. Den
har en bred Basis, hvis ophøiede Rand slutter sig til det
Sideindsnit, som findes paa den øverste Interbrachialplade,
Fig 7, d. Overfladen er lidt konvex, riflet paatvers
(mæandrisk furet) og noget nedsunken i den indre Ryghud.
Den ydre Ryghud, der som tidligere omtalt støttes
af Paxillerne, har en Mængde større og mindre, aflange
Huller (Spiracula), Fig. 14. 15. 16, a. Den bestaar af en
glat, gjennemsigtig, strukturløs Cuticula, et cellerigt Epithel
og saa den egentlige Cutis, som dannes af
Bindevævsbund-ter, der ligge i forskjellige Retninger tæt til hverandre.
Indenfor Cutis er en Bindevævshud, som er rig paa
Muskler, der krydse hverandre, og som især samle sig omkring
de førnævnte Aabninger, Fig. 14. 15. 16, b. Denne
Muskelhud, der er beklædt med et cilierende Epithel,
strækker sig ikke alene nedover de Totredjedele af
Paxillarnaa-lene, som den beklæder, Fig. 15, c, men ogsaa udover de
aflange Aabninger, som derved paa den indre Side faar en
uregelmæssig Form, Fig. 16. 15, d. Saavel omkring disse
Aabninger som omkring de halvmaaneformige Aabningers
Rand er Celleepithelet stærkt fortykket, Fig. 14, c, men
nogen Ringmuskel findes ikke omkring dem.
Hullerne (Spiracula) i Ryghuden med den
ovenomtalte Muskelanordning og de semilunære Ventralaabninger
med deres eiendommelige Klapper, kunne lukkes og aabnes
efter Omstændighederne og staa aabenbart i
Aandedræt-tets Tjeneste. Noget lignende finder ogsaa Sted hos Slæg-
and nearly at the middle, an acuminate calcareous spine
projects in an outward direction (Pl. XIII, fig. 2, c. 5.
11, h) and is observed, between the two long calcareous
needles on the actinal surface. Immediately above the
inner spherical prominence which serves as a support for
the transverse process of the ambulacral plates," two rather
long calcareous needles project, and are directed inwards,
towards the ventral furrow, covering it, for half of its
breadth (Pl. XIII, fig. 2, a. 5. 13, d). Both of these
spines are furnished with concave articulator)’ surfaces,
corresponding with the two small round prominences of
the adambulacral plates mesial part. Besides these three
articulating spines, yet a fourth spine is found, on a great
many of the inner adambulacral plates; situated about
midway between the two large marginal spines. This spine
is rather short and has a broad base. The first pair
of adambulacral plates interunite with the
corresponding ones from each adjoining ray, and form, thus, the five
oral angle plates. These are thick, strong and oblong,
with a suture along the mesial line, and they are
furnished with six long (3 on each margin) acuminate
articulating calcareous spines (teeth) which face inwards towards
the oral aperture (Pl. XIII, fig. 2).
At the base of the large dorsal chamber, the
mad-reporite is seen, seated in an interbrachial space at the
origin of a ray (Pl. XIII, fig. 7, i). It is ovate in shape,
with’ it’s broad part turned inwards, and it has a broad
base, whose elevated margin joins the lateral incision
observed on the superior interbrachial plate (Pl. XIII, fig.
7, d). The superior surface is slightly convex, ridged
transversely, and intersected by meandering furrows. It
is somewat depressed in the inner dorsal integument.
The outer dorsal integument is, as previously stated,
supported by the paxillæ, and has a multitude of larger
or smaller, oblong pores in it (spiracles) (Pl. XIII, fig. 14.
15. 16, a). It consists of a smooth transparent
structureless cuticle, and a compact cellular epithelium, besides the
genuine cutes formed of bundles of connective tissue
distributed close to each other, but extending in different
directions. Inside the cutes, there is a membrane of
mus-culous connective tissue, in which muscles cross each other,
and the muscles are especially centred around the
previously mentioned apertures (Pl. XIII, figs. 14. 15. 16, b).
This muscular integument is clad with a fimbriate
epithelium, and extends, not only, down over two third parts of
the paxillar needles included by it (Pl. XIII, fig. 15, c)
but also, out over the oblong apertures, and these obtain in
this manner, an irregular form upon the inner margin (PI.
XIII, fig. 16. 15, d). Both, around these apertures, as
well as, around the margins of the crescent formed
apertures, the cellular epithelium is greatly tumified (PI.
XIII. fig, 14, c) but no annular muscle is found about it.
The pores (spiracles) of the dorsal integument and
the semilunar ventral apertures, with their peculiar flaps,
can be shut or opened by means of the above described
muscular arrangement according to circumstances, and
clearly pertain to the respiratory system. Something sim-
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