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37
synes at være ligeligt fordelte overalt, naar Dyret lever og
er i fuld Vigør, Fig. 12. De ligge, naar Kroppen er
udspændt, et ganske lidet Stykke fra hverandre, men nærme
sig under Kontraktionerne; er Huden stærkt
sammentruk-ken, hvilket i Regelen er Tilfældet, naar Dyret har været
opbevaret i Spiritus, saa ligge Hjulene lagvis paa
hverandre; Huden faar da et sølvglindsende Udseende og føles
haard.
De store Hjul, Fig. 12, a, ere i størst Mængde
tilstede, ere sammensatte af en Centraldel, der er flad, glat,
og hvorfra udgaa Radier, hvis Antal varierer noget fra
8— 11; men hyppigst er der dog 8. Disse Radier have en
vingeformig Udvidning, Fig. 13, a, der er bredest paa
Midten, hvorved de trekantede Mellemrum blive betydelig
indknebne i den indre Halvdel, Fig. 13, b. Peripherien er
sammensat af saamange Stykker, som der er Radier, og
fra hvert saadant Stykkes ydre Rand udgaar en lang Tand,
der er bred ved sit Udspring, men ender temmelig .spids,
Fig. 13, c. Tanden har en Retning udad og nedad.
Hjulets Peripheri er saaledes besat med et Antal Tænder, der
svarer til Radiernes Antal, og disse Tænder vende indad i
Huden. Hjulet er paa Grund af Tændernes Stilling
konkavt paa dets indre Flade, imedens dets ydre er plan.
Disse Hjul variere lidt i Størrelse; saaledes er
Tverdiame-teren fra Peripheriens ydre Rand paa den ene Side til det
tilsvarende Punkt paa den anden Side fra 0.220—0.290"™;
Tverdiameteren med Tænderne udgjør fra 0.320—0.350"".
Tændernes Længde 0.080"".
De smaa Hjul ligge hist og her spredte imellem de
store, Fig. 12, og ere meget forskjellige fra disse. De
sidde paa en kort Stilk, lig dem hös Myriotrochus Rinkii.
Centraldelen (Umbonen) er saagodtsom plan, men har en
rund Knop paa Midten, hvortil Stilken er fæstet, Fig. 14.
Fra Centrum udgaa i Regelen 11 Straaler, der ligeledes
har en vingeformig Udvidning, Fig. 14, a, der ikke er saa
bred, som paa de store Hjul, men som er tilstrækkelig til
at give Mellemrummene et eget Udseende, Fig. 14, b.
Hjulets Peripheri bestaar af ligesaa mange Stykker, som
Radiernes Antal udgjør. Fra hvert Stykkes indre Rand
udgaa i Regelen 2 korte, trekantede Tænder, Fig. 14, c.
Disse Hjul ligne meget Kalkhjulene hos Myriotrochus
Rinkii; men Forskjellen er dog iøjnespringende, idet Radierne
ere noget anderledes byggede, og Tænderne , ere baade
kortere og i omtrent dobbelt saa stort Antal tilstede som hos
Rinkii; hos begge er den ydre Flade skaalformig. Ogsaa
disse Hjul variere noget i Størrelse, fra 0.071—0.098"" i
Tversnit. Tænderne ere 0.013"" Lange. Hos Myriotrochus
vare Hjulene 0.233"" i Tversnit; Tanderne 0.049"" lange.
and in such manner as. it would seem, to be equally
distributed. so long as the animal is alive and in a perfectly
healthy state, fig. 12. When the body is expanded, a
minute space intervenes between them, but on its contraction,
tbey approximate; if the skin is much shrunk, which is
generally the case after the animal has been preserved some
time in spirits, these spicules lie one above the other in
layers; the skin then acquires a glittering, argenteous
appearance, and is hard to the touch.
The large wheel-shaped spicules, flg. 12, a, are the most
numerous ; they consist of a central portion, which is flat,
smooth, and from which issue radii, varying in number from 8 to
11; most frequently, however, there are 8. These radii, or
spokes, have a pinnated expansion, fig. 13, a, broadest in the
middle, and thus reducing in extent the inner half of the
triangular interstices, fig. 13, b. The periphery is composed
of as many segments as there are radii, and from the outer
margin of each segment projects a long denticle, broad at its
origin, but terminating in a comparatively sharp point, fig.
13, c. The denticles are directed outwards and downwards.
The periphery has accordingly a number of denticles
corresponding with the number of its radii, and these
denticles extend inwards into the skin. From the position of
the denticles, the inner surface of the spicule is concave;
the outer surface is plane. These large wheel-shaped
spicules vary somewhat in size; the transverse diameter,
measured from the outer margin of the periphery on
one side to the corresponding point on the other, is
from 0.220w" to 0.290""; the transverse diameter, including
the denticles, ranges from 0.320"" to 0.350"". The length
of the denticles is 0.080"".
The small wheel-shaped spicules lie scattered here and
there among the large ones, fig. 12, from which they differ
materially in form. They are attached to a short stem, as in
Myriotrochus Ritikii. The central portion (umbo) is almost
flat, but furnished in the middle with a round knob, to
which the stem is webbed, fig. 14. From the centre
proceed, as a rule, 11 rays, likewise with pinnate expansions,
fig. 14, a, not so bçoad as that in the large spicules,
but of sufficient size to change the appearance of the
interstices, fig. 14, b. The periphery of the spicules consists
of as many segments as there are radii. From the inner
margin of each segment project as a rule 2 short triangular
denticles, fig. 14, c. These spicules present considerable
resemblance to the wheel-shaped spicules in Myriotrochus
Rinkii, but are readily distinguished from the latter,
having a somewhat different structure; the denticles, .too,
are shorter, and their number about twice as great as in
Rinkii; in both species the outer surface is cup-shaped.
These smaller spicules, too, vary somewhat in size, their
transverse diameter ranging from 0.071"" to 0.098™". The
denticles measure 0.013"" in length. In Myriotrochus, the
transverse diameter of the spicules was 0.233"", the length
of the denticles 0.049"".
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