ANATOMY OF THE KING-CRAB. 299 
The heart is tubular, with eight pairs of valvular openings 
for the return of the venous blood which flows into the 
pericardial sac from all parts of the body ; the arterial blood 
Fig. 265.—Nervous and part of the circulatory system of Limulus polyphemus, the 
King-Crab. a, vent ; «, esophagus ; 0, brain; o, nerve to the smaller eyes; o/, nerve 
to the larger eyes ; s, nerve-ring around the cesophagus. All the nerves are surround- 
ed by an arterial coat.—After Milne Edwards. 
is sent out from the arteries branching from the front end 
of the heart flowing around the upper side of the edge of the 
cephalo-thorax through numerous minute vessels. Also there 
are a pair of branchial arteries, and two arteries in the base of 
the spine. 
