ANATOMY OF THE XING-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 



.as 



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

 King-Crab, a, vent ; a, oesophagus ; b, brain ; o, nerve to the smaller eyes ; <X, nerve 

 to the larger eyes ; s. nerve-ring around the oesophagus. All the nerves are surrouiid- 

 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. 



