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 oif another branch which 



runs into the epimeron (ep. art.), it unites with an artery 



(i) 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 



bifurcating, 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 ganglion (per. g.), and the 



inferior artery the anterior side of the ganglion. The aorta 



then bifurcates. Each branch, besides giving off numerous 



small arteries, which can be better understood by reference 



to the figure (PI. III., fig. 2), gives off a large antennary 



artery {ant. art.), and is then continued as the facial 



* Contractile vascular saos 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. 



