CIRCULATION IN INSECTS. 221 



the main current, which, after 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 conveyed 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 appear to be 

 continuous- These are distinct canals, and not 

 portions of the great abdominal cavity, for their 

 boundaries are well defined ; yet not sufficiently 

 circumscribed to entitle them to the appellation of 

 vessels, for they allow the blood contained in them 

 to escape into that cavity, and mix with the portion 

 previously 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 

 antennae, the circulation is carried on by means of 

 vessels, which are continuous with the lateral canals 

 of the body; branching off from them in the form 

 of loops, ascending on one side, and then turning 

 back to form the descending vessel, so that the 

 currents in each move in contrary directions. Fig. 

 3.37 represents the appearance of these parallel ves- 

 sels in one of the antennae of the Seinblis viridis, 

 magnified thirty times its natural size. The whole 

 system of circulating channels in that insect, of 

 which the former is only a detached part, is shown 

 in Fig. 33B, where the course of the blood is indi- 

 cated by arrows ; a, representing the currents in 

 the antennae ; w, those in the rudimental wings ; 

 and T, those in the tail ; in all which parts the ves- 



