SEA-FISHERIES LABORATORY. 207 



The circulation is wholly lacunar, and simply consists 

 of broad, irregular streams passing through the spaces 

 left among the internal organs, and between the connec- 

 tive-tissue bands of the body-wall. These streams have in 

 general certain definite directions, but they are not 

 uniform, continuous currents. The fluid advances by 

 successive jerks, depending upon the movements of the 

 alimentary canal and, in part, of the reproductive system. 

 The blood is a clear fluid, containing numerous colourless 

 corpuscles. The corpuscles vary in size and shape, and 

 can accommodate themselves in diameter to the spaces 

 through which they pass. 



Plate II., fig. 2, shows the course of the main blood 

 currents. Starting from behind the eye, there are two 

 currents passing posteriorly, one flowing to each postero- 

 lateral angle of the cephalo-thorax, where it turns and 

 courses forward along the lateral margin of the carapace 

 till it reaches the group of muscles connected with the 

 mandibles. It then divides, one portion continuing along 

 the margin to the base of the antennules, where it splits 

 up into minute currents, all converging to the base of the 

 mouth, while the other branch of this cephalo-thoracic 

 current passes along the muscles of the mandibles and 

 duct of the digestive gland, and meets the currents of the 

 former branch at the base of the mouth. 



A second main current courses posteriorly through the 

 cephalo-thorax and the fourth thoracic segment, into the 

 genital segment. It flows there along the reproductive 

 organs in a broad stream, and turns round at the end of 

 the segment. The currents from both sides meet in the 

 middle line, and flow forward under the alimentary canal. 

 In the region of the second maxillipede, this median 

 ventral current breaks up into a complicated series of 

 smaller currents, some of which pass into the two currents 



