‘Branchialfodder. 
97 
bagerste Strom. Begge modes ved det dorsale Liga- | anterior stream, and one considerably longer pos- 
ment, hvor de boier om indad og udtommer sit Blod, 
sammen med det fra Hovedet tilbagevendende, i den 
forreste Del af Hjertet gjennem dettes Iste Par 
Spaltaabninger. De ovrige 3 Far Spaltaabninger 
synes at optage det Blod, der, efterat have circuleret 
i Fodderne, vender tilbage til Hjertet. 
Respirationsapparat.-— Rent morphologiskt maa 
vistnok Foddernes Epipoditer ansees som de egent- 
lige Respirationsorganer, da de aabenbart svarer til 
Gjellerne hos hoiere Krebsdyr. Men da ogsaa de 
ovrige Dele af Fodderne viser en lignende over- 
maade delikat Struktur, har man Grund til at an- 
tage, at Respirationen ikke er udelukkende ind- 
skrenket til hine Vedheng, men foregaar overalt 
paa Foddernes Overflade, hvad der ogsaa har givet 
Anledning til den almindelig benyttede Benzvynelse 
Som det physiologiskt vigtigste 
Respirationsorgan maa vi dog utvivlsomt anse selve 
Skallen, i hvilken der, som ovenfor anfort, finder 
en meget livlig Blodcirculation Sted. Ved Foddernes 
rhytmiske Bevegelser sker der nemlig en stadig For- 
nyelse af Vandet indenfor Skallen, og da dette Vand 
umiddelbart beskyller den serdeles delikate Mem- 
bran, der bekleder Valvlerne indvendigt, synes alle 
Betingelser at veere tilstede for at en hurtig Gas- 
udvexling her kan ske med det indenfor Membranen 
strommende Blod. 
Nervesystemet. — Den i Hovedet beliggende 
Del af Nervesystemet er ikke vanskelig at obser- 
vere paa tilstrekkelig gjennemsigtige Exemplarer. 
Den bestaar af det saakaldte ovre Svelgganglion, 
eller Hjernegangliet, med de fra samme udgaaende 
Nerver. Selve Hjernegangliet er ikke af serdeles 
betydelig Storrelse, og ligger (se Tab. XV, Fig. 2) 
‘temmelig langt tilbage i Hovedet, umiddelbart bag 
det enkle Wie, hvormed det forbinder sig med en 
temmelig bred Fortsats (se ogsaa Tab. XVI, Fig. 9, 
10). Det bestaar, som sedvanlig, af 2 symetriske, 
med hinanden i Midtlinien forbundne Halvdele, 
hvoraf enhver er udtrukket i 2 divergerende, koni- 
ske Fortsatser. Fra de forreste Fortsatser udgaar 
de overordentlig lange og sterke Synsnerver og 
desuden en ganske liden Nerve for Giemusklerne. 
Selve Synsnerverne passerer fortil ind i Hovedets 
Pandedel, hvor enhver af dem svulmer ud til et 
kolleformigt Synsganglion. Begge Ganglier ligger 
tet sammen, uden dog at smelte sammen, og deres 
Ender er kun ubetydeligt fjernet fra de sammen- 
satte Wine (se Fig. 10). Fra dem udgaar talrige 
fine Nervefibre, der trenger ind i Minene og for- 
binder sig med disses enkelte Synselementer. De 
bagre Fortsatser af Hjernegangliet (a') er noget 
kortere end de forreste og mere udadrettede (se Fig. 
10), men af en lignende konisk Form. De giver 
13 — G. 0, Sars: Fauna Norvegizx. 
terior one. They meet at the dorsal ligament, where 
they turn inwards, and empty their blood, together 
with that running back from the head, into the an- 
terior part of the heart through that organ’s first 
pair of ostia. The 3 other pairs of ostia appear to 
receive the blood which, after having circulated in 
the legs, returns to the heart. 
Respiratory Organs. — From a purely morpho- 
logical point of view, the epipodites of the legs 
must be considered as the true respiratory organs, 
as they evidently answer to the gills in higher 
Crustaceans. But as the other parts of the legs 
also show a similar exceedingly delicate structure, 
there is reason to suppose that the function of 
respiration is not confined exclusively to these 
appendages, but is carried on over the entire sur- 
face of the leg, a circumstance which has given rise 
to the generally used term — branchial legs. As 
the physiologically most important organ of respi- 
ration however, we must undoubtedly regard the 
shell itself, in which, as stated above, a very active 
circulation of the blood goes on. By the rhythmical 
movements of the feet, a constant renewal of the 
water inside the shell takes place, and as this water 
is in immediate contact with the peculiarly delicate 
membrane lining the interior of the valves, all the 
conditions requisite for a rapid exchange of gas 
with the blood flowing within the membrane, appear 
to be present. 
Nervous System. — That part of the nervous 
system lying in the head is not difficult to observe 
in sufficiently transparent specimens. It consists 
of the so-called supra-cesophageal ganglion or cere- 
bral ganglion, with the nerves proceeding from it. 
The cerebral ganglion itself is of no very consider- 
able size, and is situated (see Pl. XV, fig. 2) rather 
far back in the head, immediately behind the ocel- 
lus, with which it is connected by a_ tolerably 
broad projection (see also Pl. XVI, figs. 9, 10). It 
consists as usual of 2 symmetrical halves connected 
with one another in the median line, each half 
being drawn out into 2 divergent conical protuber- 
ances. From the foremost of these issue the excee- 
dingly long and strong optic nerves, as also a very 
small nerve for the ocular muscles. The optic 
nerves themselves pass forwards into the frontal 
part of the head, where they each swell out into a 
club-like optic ganglion. These ganglia lie close 
together without however coalescing, and their 
extremities are at only a slight distance from the 
compound eyes (see fig. 10). Numerous delicate 
nerve-fibres issue from them, entering the eyes, and 
connecting themselves with the several visual ele- 
ments of those organs. The hind protuberances of 
the cerebral ganglion (a') are rather shorter than 
‘the front ones, and directed more outwards (see 
