CIRCULATION IN INSECTS. 



175 



being discharged from the anterior extremity of the dorsal 

 vessel, descends in a wide spreading stream on each side 

 and beneath that vessel, another portion of the blood is con- 

 veyed by two lateral trunks, which pass down each side of 

 the body, in a serpentine course, and convey it into the 

 lower extremity of the dorsal vessel, with which they are 

 continuous. These are decidedly vessels, and not portions 

 of the great abdominal cavity, for their boundaries arc 

 clearly defined; yet they allow the blood contained in them 

 to escape into that cavity, and mix with the portion previ- 

 ously diffused. All these wandering streams sooner or later 

 find their way into the dorsal vessel, being absorbed by it 

 at various points of its course, where its membranous coat 

 is reflected inwards to form the valves. In the legs, the 

 tail, and the antennas, the circulation is carried on by means 

 of vessels, which are continuous with the lateral vessels of 

 the body, branching off from them in the form of loops, as- 

 cending on one side, and then turning back to form the de- 

 scending vessel, so that the currents in each move in con- 

 trary directions. Fig. 337 represents the appearance of 



c.-.. - -^x ^ — * 



^^^::":^>'''^•r■^r■•■.,^^•^^^'::i'■^^^^^^^ 



these parallel vessels in one of the antennae, of the Seynhlis 

 viridis, magnified thirty times its natural size. The whole 



