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29
Vi have vel seet, at baade Ryg- og Bugkarret afgive
Grene til Tarmen, Mesenteriet og til Æggestokken; men
vi have ikke kunnet iagttage nogen Forbindelse imellem
dem, og langtfra den netformige Karüdbredning paa
Tai*-men, som’ Schmarda angiver at være tilstede hos Bonellia
viridis.
Der er hos Hamingia vistnok et afsluttet Kredsløb;
men det er et Spørgsmaal, om dette ikke er dobbelt,
saaledes nemlig, at den Gren af Ryg- og Bugkarret, Fig. 14,
i, e, der fra den forreste store udbredte Karforgrening,
Fig. 14, g, løber langs Tarmens Sider til bag imod de
sidste Circumvolutioner, — om ikke disse Kar paa en lignende
Maade udbrede og forene sig som ved den store
Karforgrening; er dette Tilfældet, saa er der et andet Kredsløb,
der jo er meget længere end det første. Men hvilket af
disse Kar, der virker som Arterie eller Vene, det lader sig
vanskelig afgjøre. Kan det antages, at det flotterende,
muskuløse Legeme virker som et Hjerte, kan dette
betragtes som et Centralorgan, da forekommer det os, at
Bugkarret, med hvilket Hjertet staar saagodtsom i
umiddelbar Forbindelse, maa repræsentere det arterielle System, og
følgelig Rygkarret Yenesystemet. Dette synes yderligere at
bekræftes derved, at Bugkarret, der er tykkere, har fastere
muskuløse Vægge, end Rygkarret.
Sammenligner man nu Circulationsorganerne hos vort
Dyr med Bondliens, saa viser det sig, at de afvige noget,
hvilket ogsaa var at vente, alene af den Grund, ut
Hamingia ingen Snabel har; men Fællesskabet er ikke
destomindre temmelig iøinefaldende. Hos Bonellien er den
sæk-formige Udvidning af Bugkarret, der flotterer i den
midterste Del af Kropshulheden, udtydet som muligens et
pulserende Centralorgan (Hjerte, Lacaze-Duthiers), og
forsaavidt kan det ansees som et Analogon til det særegne Organ
hos Hamingia, som vi have fundet flotterende i den forreste
Ende af Kropshulheden, og som staar i Forbindelse med
Bugkarret. Men omtrent paa det Sted, hvor
Lacaze-Duthiers har fundet den sækformige Udvidning af Bugkarret,
der findes hos Hamingia den særegne Karforgrening, der
danner Foreningen imellem Ryg- og Bugkar, hvilken ikke
kan betragtes som nogen Centraldel, men snarere som et
peripherisk Afsnit af Circulationen. ■
Nervesystemet.
Hos Gephyreerne ialmindelighed er Nervesystemet
temmelig let tilgjængelige og anderledes er det heller ikke
hos vor nye Slægt. ’ %
Naar Tarmrøret er borttaget eller skudt til Side, saa
fremtræder tydeligt Centralnervestrængen, der langs Midten
af Bugfladen strækker sig fra Munden til Anus, Fig. 16, a.
Den har en hvid glindsende Farve, er bundet til
Bugmesen-teriet, og er beklædt paa sin indre i Kropshulheden
fremragende Flade af Peritoneum. Den ligger altsaa imellem
dette og Skraamuskellaget.
Branches proceeding from the dorsal and ventral
vessels to the intestine, the mesentery, and the ovarium, we
have observed, but have failed to detect any connexion
whatever between them; we certainly did not observe the
reticulating vascular expansion on the intestine alleged by
Schmarda to occur in Bonellia viridis.
Hamingia is unquestionably furnished with a true
circulatory system; but the question arises, whether that
system be not bifold, inasmuch as the branches of the
dorsal and ventral vessels, fig. 14,- i, e, which, issuing from
the greatly expanded anterior vascular ramification, fig. 14,
g, protend backwards along the sides of the intestine to
the last circumvolutions, may possibly in turn expand and
unite, precisely as do the vessels at the great vascular
ramification. Now, assuming this to be the case, a new
circulation will commence, taking another and much longer
course. But which of the said vessels conveys venous, and
which arterial blood, is indeed difficult to decide. If,
however, the floating muscular body be assumed to perform the
function of a heart — be regarded as a central organ, the
ventral vessel, with which it directly communicates, might,
we think, with good reason be held to represent the
arterial system, and the dorsal vessel the venous. And this
view would seem to derive additional support from the
fact of the ventral vessel, which is thicker, having more
compact and muscular walls than the dorsal.
On comparing the circulatory organs in Hamingia
with those in Bonellia, they are certainly found to differ
somewhat, which was indeed to be expected, if for no other
reason, because of the former not having a proboscis; but
their mutual resemblance is nevertheless striking. The
saclike expansion of. the ventral vessel floating in Bonellia in
the middle of the perivisceral cavity, has been held to
represent, possibly, a pulsating central organ (heart,
Lacaze-Duthiers), and in that sense it may be regarded as the
analogue of the organ in Hamingia found floating at the
anterior extremity of the perivisceral cavity, and which is
connected with the ventral vessel. Now, about in the place
where Lacaze-Duthiers observed the sac-like expansion of
the ventral vessel, occurs in Hamingia the vascular
ramification, connecting together the dorsal and ventral vessels,
— which can hardly be a central part, but should rather
be regarded as a peripheral section of the circulatory system.
Nervous System.
In the Gephyreæ, the nervous system is as a rule
easily accessible, — an assertion which also holds good of
our new genus.
On removing or pushing aside the intestinal canal,
the central nervous chord — of a lustrous white — is
distinctly visible, protending along the middle of the ventral
surface from mouth to anus, fig. 16, a. It is webbed to
the ventral mesentery, and invested on its inner sui’face,
which projects into the perivisceral cavity, with peritoneal
membrane. It extends accordingly between the peritoneum
and the oblique muscular layer.
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