KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 52. N:o IG. 39 
rectal region, the largest being the right one. From the left lobe emanates the 
anterior aorta (a.), separated by a valvule from the ventricle, and from the posterior 
side of the central ventricular portion, somewhat to the right of the median line, the 
posterior aorta appears. As to the anterior aorta, this runs subcecutaneously in the 
left body side out of the stomach and the oesophagus. From its oesophageal por- 
tion it gives off a branch (a. g.) to the upper part of the duodenum, which branches 
on the one hand to the hinder side of the stomach and to the intestine, and on 
the other gives rise to two vessels running along each side down the duodenum. In 
Chamostrea, thus, the arteria gastrica emanates in a quite different manner from that 
in Chamidae (cf. above). Close above the mouth, the anterior aorta bifurcates into 
1) a branch penetrating on the left side of the oesophagus forewards to the anterior 
adductor and the mantle (no corresponding vessel occurs on the right side) and 
2) the arteria pedalis, which follows the pedal nerve cords down into the foot. — 
The posterior aorta runs between the two nephridia down on the anterior side of 
the adductor posterior and sends out a vessel which follows the under side of the 
rectum posteriorly. 
The venous blood system begins among the viscera, from where two principal 
trunks converge towards the region of the mouth; an upper one from the umbonal 
region and a lower one from the foot. 'To the lacunae that are formed by them on 
each side of the oesophagus also join veins from anterior adductor and mantle. 
From the oesophageal region the blood is carried away by a trunk (v. c.) running 
laterally along each body side, the largest one being the left, and this debouches 
directly into the renal sinus on the base of the gill axis. Before its entrance here 
it receives veins from below. 
This lateral vein is homologous to that vessel in Chama, which runs beneath 
the fixation line of the exterior lamella of the anterior demi-branch and, further 
back, is contained in the free margin of the reflected lamella. Which condition may 
be the primary one, that of Chama or of Chamostrea, is a question impossible to 
answer until a comprehensive inquiry into the circulation within the lamellibranchs 
has been carried out. 
From the hindermost part of the body all venous blood is carried away to the 
renal sinus and from there arrives directly into the gills (cf. fig. 6, s. r.). 
The mantle has its own closed circulation inasmuch as a special pallial vein 
(v. p.) leads the blood from the upper part of the mantle directly into the auricles. 
The genital organs. Chamostrea is hermafroditie. The uppermost part of 
the visceral hump is occupied by the ovarial folliculi, which penetrate somewhat 
backwards between the rectum and the pericard. Down on the side they reach about 
the lateral vein. The present specimen had great masses of mature eggs, the largest 
measuring 0.17—9.20 mm, and each surrounded by a thick cuticula. 
Somewhat below the lateral vein the spermatoid folliculi begin to appear, but 
they pentrate farther upwards in the surroundings of the intestine. They also were 
filled with wholly developed genital products. 
Hermaphroditism is a peculiarity that Chamostrea shares with all other Anatin- 
