Vin] THE CIRCULATORY SYSTEM 165 



older nymphs, blood circulates in the spaces around the tracheae 

 of the developing wing. 



On entering the abdomen, the circulation becomes rather 

 sluggish. The weak dorsal stream passes slowly backwards along 

 either side of the heart. Most of its corpuscles pass into the heart 

 in the eighth segment. Ventrally, a somewhat stronger stream 

 passes along either side of the abdomen, as well as medially above 

 the nerve-cord. This stream passes right back to the anus, and, 

 in the Zygoptera, bathes the bases of the caudal gills. It then 

 turns upwards and forwards, entering the heart through both 

 chambers of the hind-heart. 



As the larva grows, the haemocoele extends further into all 

 the appendages, so that blood can circulate for a considerable 

 distance into the antennae, the legs, and the caudal gills of the 

 Zygoptera. 



