AN A TO Ml' OF TUB KING-CRAB. 319 



The heart is tubular, with eight pairs of valvular openings 

 for tlie return of the venous blood which iiows into the 

 pericardial sac from all parts of tlie body ; tlie arterial blood 



Fig. 270. — Nervous and part of the circulatory system of Limulus polyphemn^, the 

 Kin2:-Crab. a, vent ; ff, cesophagus ; b, brain ; o, nerve to the smaller eyes ; 0\ nerve 

 to the larger eyes ; s, nerve-nng around the cfisophagus. All the nerves are surround- 

 ed by an artenal 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. 



