LIGIA. 83 
and run outwards at right angles. Each gives off a large 
branch which supplies the walls of the stomach, a branch 
running to the hepatic tubules, a few small arteries to the 
soft parts, and, after giving off another branch which 
runs into the epimeron (ep. art.), it unites with an artery 
(1) which is the anterior prolongation of the lateral artery. 
Immediately on entering the cephalic segment, a small 
median unpaired artery arises on the dorsal side, and 
bifureating, runs in the hypodermis. In front of this the 
aorta gives off a pair of ophthalmic arteries (op. a.) which 
run outwards to the eyes, giving off many small branches 
to the soft parts. The aorta now bends down in front of 
the stomach, where it dilates somewhat, the dilation lying 
in a cavity on the anterior face of the stomach. This 
dilation serves as a kind of cephalic ‘heart,’ as it has 
on each side muscles connected with a pair of chitinous 
rods from the anterior face of the stomach. These muscles 
will aid in the contraction and dilation of the cephalic 
‘heart,’ and so help to pump the blood into the rest of 
the vessels of the median dorsal aorta; the blood, on 
account of the posterior position of the heart, would not 
be driven into these vessels so effectively, if it were not 
assisted by the action of the cephalic heart.* At the point 
where the aorta bends, it gives off dorsally a small median 
artery, and lower down two median unpaired arteries, 
each of which bifurcates, the superior one supplying the 
posterior side of the cerebral ganghon (cer. g.), and the 
inferior artery the anterior side of the ganglion. The aorta 
then bifureates. Hach branch, besides giving off numerous 
small arteries, which can be better understood by reference 
to the figure (Pl. III., fig. 2), gives off a large antennary 
artery (ant.art.), and is then continued as the facial 
* Contractile vascular sacs occur in the heads of certain insects. 
Pawlowa (1895) has described them in the heads of certain Orthoptera, 
and, according to Selvatico, they occur in certain Lepidoptera. 
