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32
i de mest forskjellige Former, fra 2-armede indtil 7-armede,
fremgaar, at Delingen foregaar temmelig Langsomt. Alt
eftersom Spalten bliver dybere og videre, reproducerer
Skiveranden smaa, aflange Kalkstykker, hvorved den
saagodtsom ganske lukkes. Paa Hudskelettet sees dette tydeligst,
idet de nyproducerede Kalkplader ere baade mindre end
de gamle, staa længere fra hverandre, og bære kun en Pig,
imedens de gamle paa den øvrige Del af Skiven bære mange
Pigge. Afsnøringen foregaar paa Bugfladen, først efterat
den nysomtalte Proces er tilendebragt paa Rygsiden, og da
paa den Vis, at de to første Par Adambulacralplader og
Ambulacralpladerne med de to inderste Fødder blive
tilbage. Fra det andet Par Adambulacral- og Ambulacralplader,
samt fra den omgivende Hud, udspringer en liden, knap
en halv Millimeter lang, konisk, blød Knop, i hvis* Hud
findes spredte Kalkkorn; men endnu ingen Skeletdannelse.
Paa et Exemplar, der havde kastet 2 Arme, saaes to
saadanne Knopper, der vare omtrent lmm lange, og her
iagttoges et tydeligt Anlæg saavel til Hudskelet som
egentlig Skelet, saaledes kunde ved nogen Forstørrelse sees baade
Adambulacral- og Ambulacralpladerne, ligesom den ydre
Hudflade var besat med enkeltstaaende Pigge. Imellem
disse to smaa Arme saaes Begyndelsen til en 3die Arm.
I en fraskilt Arm fandtes to Blindtarme, der ved
korte Bindevævstraade vare bundne til Ryghudens indre
Væg, samt endel af Generationsorganet.
Hvorvidt de fra Moderlegemet fraskilte Arme
individualisere sig, hvorvidt Reproduktionsevnen hos dem er istand
til at danne Skive og Armer, med deri indesluttede
Organer, kunne vi ikke med fuld Sikkerhed afgjøre; men
Sandsynligheden for en saadan Reproduktionsevne forekommer
os at være stor, idet Dele af Mavens Udkrænkninger, der
danne Blindtarme, fulgte med den fraskilte Arm, og vare
paa det Exemplar, hvori vi iagttog Begyndelsen til
Fra-skillelsen, bundne ved nydannede Bindevævstraade til
Hudens indre Væg. Med Hensyn hertil har E. Haeckel først
med Bestemthed udtalt sig for den Mening, at en saadan
Reproduktion virkelig finder Sted, hvilken Mening han
støtter paa Iagttagelser anstillede paa Slægten Ophidiaster, og
som ere offentliggjorte i en særdeles interessant
Afhandling1. Her er dog at bemærke, at hos Ophidiaster
fraskilles ikke den hele Arm, saaledes som Tilfældet er hos
Stichaster albulus, men en Stump af nogle Millimeters
Længde bliver tilbage og rager udenfor Skiven, og fra
denne Stump sker Reproduktionen. Kan altsaa en saale-
1 E. Haeckel. Die Kometenform der Seesterne und der
Generation s wechsel der Eehinodermen. ^eitsch. f. Wiss. Zoolog. 30ter
Band, Supplement, pag. 424.
the most varied forms, ranging, from 2-rayed, up to 7-rayed
specimens; it appears that the division proceeds rather
slowly. According as the fissure becomes deeper and wider,
the diskal margin reproducés small, oblong, calcareous
ossicles, by which the fissure becomes almost closed. This
is most distinctly seen in the dermal skeleton, because, the
newly produced calcareous ossicles, are, both, placed
further apart, and are smaller, than the old oneç, and they carry
only one spine, whilst, the old ossicles of the remainder of
the disk carry numerous spines. The constrictive
separation proceeds first on the ventral surface, after the process
just spoken of is concluded on the dorsal surface, and
then, in such a manner, that the first pair of adambulacral
and ambulacral plates, with the two inmost suckers, are
left behind. From the exterior pair of these
adambulacral and ambulacral plates, as well also, as from the
surrounding integument, there springs, a small, barely half a
millimetre long, coniform soft knob, in whose integument
scattered calcareous grains are visible, but not as yet any
skeleton formation.
In one specimen which had cast two rays, two such
knobs were visible, measuring about 1 millimetre long, and,
there was, here, visible, a distinct tendency to formation of
both, a dermal skeleton, as well as, a skeleton proper.
With the assistance of a magnifyer, both adambulacral
plates could thus be seen, whilst also, the exterior
integu-mental surface was seen to be beset with spines, placed
singly. Between these two small rays, the commencement
of a third was perceptible.
In a separated ray, 2 cæca were found, which were
united to the inner wall of the dorsal integument, by short
filaments of connective-tissue, and, also, by a portion of the
generative organ.
In what degree the rays separated from the parent
body become individualized, or, in what degree the
reproductive energy in them is able to produce disks, and arms,
with their included organs, we have not been able to
decide with complete certainty, but, the probability of such a
reproductive capacity, appears to us to be great, because,
portions of the protrusions of the stomach forming the
cæca, accompany the separated ray, and, in the specimen
in which we observed the commencement of the separative
process, these were connected to the wall of the
integument, by filaments of freshly formed connective tissue. But
with regard to this E. Haeckel has first distinctly expressed
himself of the opinion, that such a reproduction really
takes place, and he bases his opinion, on his observations
of the genus Ophidiaster, and which he has published in
an extremely interesting memoir1. There is however to be
remarked, here, that in Ophidiaster, the whole ray is not
separated as is the case in Stichaster albulus, but a stump,
of a few millimetres in length, is left, projecting from the
1 E. Haeckel. Die Kometenform der Seesterne und der
gene-rationswechsel der Eehinodermen. Zeitsch. f. Wiss. Zoolog. 30ter
Band. Supplement pag. 424.
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