dele som hver udmunder med en kort Udforselsgang 
noget lateralt i Tarmens forreste Del, og i sin Peri- 
pheri er delt i talrige bugtede Blindsekke, ialminde- 
lighed fyldte med et intenst gultfarvet Stof. Hvert 
Organ udsender nedad en Sidegren, der i Hovedets 
ventrale Del, umiddelbart foran Basis af Overleben, 
oploser sig i flere uregelmessige Lappe. Hoved- 
massen af Organet ligger dog dorsalt, hvor det 
sammen med det tilsvarende Organ paa den anden 
Side danner en tilsyneladende sammenhengende 
Kalot over Tarmens forreste Del (se Fig. 2 og 3). 
Circulationsapparatet. — Hjertet (se Tab. XV, 
Fig. 1) er beliggende ovenover Tarmen i den forre- 
ste Del af Truncus, strekkende sig fortil ind i 
Nakkesegmentet, bagtil ind i det 4de fodberende 
Segment. Det har Formen af et fortil noget videre 
cylindriskt Ror, aabent i begge Ender, og desuden 
forsynet til hver Side med 4 tydelige Spaltaabninger, 
1 Par for Nakkesegmentet, de 3 ovrige Par for de 
3 forreste Segmenter af Truncus. Af nogen virke- 
lige Blodkar har jeg ikke kunnet finde noget Spor; 
men Blodet folger dog under sin Circulation i Lege- 
met visse meget bestemte Baner. Da Blodlegemerne 
er meget tydelige, er det ikke saa vanskeligt paa 
tilstrekkelig gjennemsigtige levende Exemplarer at 
studere de vesentligste Trek af Circeulationen, og 
jeg skal i det folgende i Korthed beskrive samme, 
saaledes som jeg har troet at finde den ved gjen- 
tagne omhyggelige Undersegelser. Fra den bagre 
Del af Legemet kommer en sterk Strom af Blod, 
der folger Rygsiden af Truncus og passerer direkte 
ind i Hjertet gjennem dettes bagre Aabning. Ved 
Hjertets Systole lukkes denne Aabning, saavelsom 
de laterale Spaltaabninger, og Blodet stedes med 
stor Kraft ud af Hjertets forreste Ende. En Del 
af den saaledes af Hjertet udkomne Blodmasse pas- 
serer direkte ind i den forreste Del af Legemet og 
forsyner Hovedet med dets forskjellige Vedheng 
med Blod. En anden Blodstrom boier pludselig om 
under Hjertet og lober bagover, umiddelbart neden- 
for den tilforende dorsale Blodstrom, lige til Hale- 
delen, hvor den synes at boie om paa Bugsiden af 
Dyret for at forsyne Branchialfodderne med Blod. 
En 3die betydelig Del af den fra Hjertet udstedte 
Blodmasse passerer til hver Side mod Skallens Lukke- 
muskel, hvor den i Omkredsen af Muskelareaen 
trenger ind i selve Skallen. Herfra fordeles Blodet 
rundt om i de to Valvler, idet det i forskjellige Baner 
gjennemstrommer det complicerede System af Hul- 
rum, der, som ovenfor anfort, findes mellem disses 
2 Lameller. Efrerat have circuleret i Skallen sam- 
ler Blodet sig lidt efter lidt i 2 dorsale Hoved- 
stromme, der lober langs Rygkanten af Skallen, 
en ganske kort forreste, og en betydelig lengere 
96 
is there also situated in the head. As in Lepidurus. 
this organ consists of two symmetrical halves each 
opening by a short excretory duct somewhat later- 
ally in the anterior part of the intestine, and 
divided in its periphery into numerous cea, gene- 
rally filled with a substance of an intense yellow 
colour. Each organ sends down a lateral branch 
which is resolved into several irregular lobes in the 
ventral part of the head immediately in front of the 
base of the labrum. The great bulk of the organ, 
however, is situated dorsally, where, together with 
the corresponding organ on the other side, it forms 
an apparently continuous cap over the anterior part 
of the intestine (see figs. 2 and 3). 
Circulatory System. — The heart (see Pl. XV, 
fig. 1) is situated above the intestine in the anterior 
part of the trunk, extending forwards into the cer- 
vical segment, and backwards into the 4th pediger- 
ous segment. It has the shape of a cylindrical 
tube, rather wider in front, and open at both ends, 
and also furnished at each side with 4 distinct ostia, 
one pair for the cervical segment, the other 3 for 
the 3 foremost segments of the trunk. I have been 
unable to find any trace of actual blood-vessels, but 
during its circulation through the body, the blood 
follows certain fixed courses. As the corpuscles are 
very distinct, it is not difficult in sufficiently tran- 
sparent living specimens to study the principal fea- 
tures of the circulation, and I will here briefly 
describe them as I have found them by repeated 
careful investigations to be. From the hind part of 
the body comes a strong stream of blood, keeping 
to the dorsal side of the trunk, and passing directly 
into the heart through its posterior aperture. This 
aperture, as well as the lateral ostia, is closed by 
the heart’s systole, and the blood is ejected with 
great force from the anterior end of the heart. A 
portion of the quantity of blood thus issuing from 
the heart, passes directly into the anterior part of 
the body, and supplies the head and its various 
appendages with blood. Another stream of blood 
turns suddenly below the heart and flows back- 
wards immediately below the afferent dorsal stream 
right up to the caudal part, where it appears to 
turn to the ventral side of the animal, in order to 
supply the branchial legs with blood. A third con- 
siderable part of the quantity of blood ejected from 
the heart, passes on both sides towards the adductor 
muscle of the shell, where, within the circumference 
of the muscular area, it forces its way into the 
shell itself. From this the blood is distributed over 
the two valves, flowing by various courses through 
the complicated system of cavities which, as stated 
above, is found between their 2 lamelle. After 
having circulated in the shell, the blood gradually 
collects in two principal, dorsal streams which run 
along the dorsal edge of the shell, one quite short 
