DISSECTING OBJECTS. 



127 



into chambers, separated from each other by valves. There are 

 also valves at the sides to receive the blood from the venous 

 sinuses of the body. But a single artery has been seen, which 

 goes to the head, dividing into three branches. It was thought 

 that the blood exuded through the vessel and found its way 

 through the body as it best could, back to the heart ; but in 

 dissecting a Limulus (king crab), Dr. Goadby traced the artery 

 into certain large sacs or vessels, evidently answering the pur- 

 pose of veins (venous sinuses). It 1s probable the same holds 



Fig. 37. 



Fig. 38. 



good of insects. Fig. 38 represents the dorsal vessel in the 

 larva of Ephemera. The arrows indicate the current of the 

 fluid. 



