ANATOMY OF THE KING-CRAB. 319 



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. 270. Nervous and part of the circulatory system of Limulus polyphemus, the 

 King-Crab, a, vent ; ce, oesophagus ; 6, brain ; o, nerve to the smaller eyee ; tf, nerve 

 to the larger eyes ; s, nerve-ring around the oesophagus. 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. 



