ten Pteraster: hos denne er ogsaa Aabninger i Ryghuden, 
p) to) to) Bite) 9 
fuldkommen lig dem hos Hymenaster, og — hvad der ikke 
tidligere har været observeret — at der hos Pteraster 
findes imellem de lange Naale, som udspænde Hudbræm- 
men, en aflang Spalte, Fig. 18,4, der dækkes af en mem- 
branøs Klappe, Fig. 18, 0, hvori en særegen, knæbøiet Pig 
ligger indesluttet, Fig. 19, hvilken er forsynet med en kon- 
kav Ledflade, Fig. 19, a, og et stærkt Muskelapparat, 
som gjør, at Klappen med Lethed kan bevæges og lige- 
som hos Hymenaster aabne og lukke Spalten. Disse Spal- 
ter, der fore ind til Ryghulen ligesom Tilfældet er hos 
Hymenaster, sees kun, naar Finnerne fjernes fra hverandre, 
Fig. 18, c, og da kun ved Loupe, uden paa meget store 
Exemplarer, hvor de kunne iagttages med blotte Øie. Igjen- 
nem disse Spalter (semilunære Ventralaabninger hos Hy- 
menaster), Spiracula og Trakten, strømmer Søvandet ind 1 
Ryggens Hulrum, hvor det kan forblive, indtil det er af- 
benyttet, idet samtlige Aabninger lukkes. Men imedens 
hos Hymenaster den egentlige (indre) Ryghud, der bedæk- 
ker Kropshulheden, er overordentlig tynd og vel skikket 
til at gjennemtrænges af Sovandet, er den indre Ryg- 
hud hos Pteraster forholdsvis meget tyk og lader derfor 
vanskeligt Søvandet passere, hvorfor der hos denne Slægt 
findes særegne hule Organer ved Grunden af Paxillerne, 
der ere fæstede i Ryghuden, som aabne sig i Krops- 
hulheden og ere homologe med Tentakelrørene hos Aste- 
riderne. Foruden at Ryggens Hulrum tjener som Respira- 
tionshule, saavel hos Hymenaster som Pteraster, tjener det 
ogsaa som Udklækningshule for Æggene, der føres gjen- 
nem en kort Kanal fra /Æggestokkene ind i Hulrummet, 
hvori Ungerne forblive under hele Embryonalperioden. 
Fordøielses- og Generationsorganerne. 
Mayen er stærkt foldet, har ti korte Blindtarme, der 
udgaa med hver sin korte Gren fra Mavesækken og lægge 
sig tæt hen til den indvendige Rand af Armenes Grund- 
del, Fig. 6, b. Fra Maven udgaar en kort men temmelig 
tyk Rectum, der aabner sig paa det førbeskrevne Analfelt. 
Den øverste Del af Maven tilligemed Rectum er bunden 
til den indre Ryghud med mange, temmelig stærke Mesen- 
terialbaand. Ved Siden af Blindtarmene findes i det tid- 
ligere beskrevne Rum, som dannes af Iste Armpaxilles 
Basaldel og Ambulacralpladerne, Kjønsorganerne, Fig. 6, ¢, 
der bestaa af en Samling smaa Blerer i Form af Drue- 
klaser. De ere temmelig faste, ganske hvide, og fra dem 
udgaa Smaagrene, som forene sig i en fælles Udførselska- 
nal, Fig. 6. Denne, der er temmelig tyk og kort, munder 
ud med en lille rund Aabning i Ryghulen paa hver Side 
af Armenes Grunddel tæt ved Armvinklerne, Fig. 6, e. 
Slegtskarakter. 
Analaabningen central i Bunden af det store Hulrum, 
79 
In that 
the apertures in the dorsal integument are exactly like 
those in Hymenaster, but, what has not previously been 
observed, is this; that in Pteraster, there is found between 
ilar also oceurs in the genus Pteraster. genus, 
the long needles expanding the integumental membrane, an 
oblong fissure (Pl. XIII, fig. 18, b). In the flap, there 
lies enclosed, a peculiar flexed spine (Pl. XIII, fig. 19), 
and this is furnished with a concave articulatory surface 
(Pl. XIIL, 19, a), and a strong muscular apparatus which 
causes the flap to be moved with ease, and like the Hym- 
enaster, to open and close the fissure. These fissures lead 
into the dorsal chamber, as is also the case in Hymenaster, 
and are only observable when the fins are separated from 
each other (Pl. XIII, fig. 18, ¢); and only then, with the 
assistance of a magnifier, except in very large specimens, 
when they may be observed with the naked eye. Through 
these fissures, (semilunar ventral apertures in Hymenaster) 
the spiracles, and the funnel shaped prominence, the 
water flows into the dorsal cavernous chamber, where it 
served its purpose, all 
the openings are closed. But, whilst, in Hymenaster, the 
real (inner) dorsal integument which clothes the body cay- 
is retained until it has when, 
ity is extremely thin, and well adapted for penetration by 
water, the inner dorsal integument in Pteraster, is propor- 
tionately very thick, and, therefore, permits the water to 
pass with difficulty. In Pteraster therefore, there are found 
special cavernous organs, situated at the base of the pax- 
illæ and opening mto the body cavity, and these are homo- 
logous with the tentacular tubés in the Asteridæ. Besides 
the dorsal cavity, in both Hymenaster and Pteraster, serv- 
ing as respiratory chamber, it serves, also, for hatching the 
ova. These are conducted to it from the ovaries, through 
a short duct, and the young starfish remain in it during 
the whole of their embryonal period. 
The organs of digestion and reproduction. 
The stomach is formed by numerous laminating folds, 
and has ten ceca, each with a short branch proceeding 
from the stomach lining, and they lie close up to the in- 
ternal margin of the origin of the rays (PI. XIII, fig. 6, 0). 
From the stomach, there proceeds a short, but rather thick 
-rectum, which opens into the previously described anal 
area. The superior portion of the stomach, together with 
the rectum, is connected to the inner dorsal integument, 
by many rather strong mesenteric ligaments. Alongside 
the ceca; in the space previously described as formed by 
the basal portion of the first paxillæ of the ray and the 
ambulacral plate; are seen the sexual organs (PI. XIII, 
fig. 6, c). These consist, of a collection of small vessicles 
or blisters, resembling bunches of grapes. They are toler- 
ably consistent, and quite white. From them there 
ceed several small branches, uniting in a common duct 
(Pl. XIII, fig. 6). This duct is pretty thick and short, 
and terminates in a small round opening into the dor- 
pro- 
sal chamber, on each side of the origin of the rays, close 
to the brachial angle (Pl. XIII, fig. 6, e). 
Generic Character. 
The anal aperture is central, and seated at the base 
