82 
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 IT., 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 
