i37 



Loop branches passing to the trunks, anterior 

 and posterior. 



Branches passing inwards and supplying 

 viscera. Branches from the first, second, third, 

 and fourth abdominal tracheae supply mainly the 

 mid-gut, those from the fourth and fifth the 

 ovaries, those from the sixth and seventh the 

 genital organs. 



The Vascular System. — As in most insects 

 where the respiratory system ramifies throughout 

 the whole body, the vascular system is not well 

 developed. A dorsal vessel or heart . and an 

 anterior prolongation of this (aorta) are the only 

 closed blood-vessels. Apart from the dorsal vessel 

 the blood circulates in large blood spaces, which 

 lie between the lobes of the fat-body and among 

 the muscles and viscera. 



The dorsal vessel passes close beneath the 

 tergal plates throughout the abdomen. It is very 

 thin walled, and is not provided with valves. The 

 upper portion is attached to the dorsum at 

 intervals by suspensory fibres (muscular), so that 

 a festooned appearance is given in longitudinal 

 section. There is, however, no true division into 

 compartments. Laterally large cells (pericardial 

 cells) are arranged throughout its entire extent, 

 and fibres of a muscular nature (alary muscle) 

 pass from the body wall and end in branches in 

 close connexion with the dorsal vessel. 



At the first abdominal segment the dorsal 

 vessel dips down beneath the mesophragma, 

 lying as it does so in direct contact with the 

 cuticule. In the thorax it again arches upwards, 

 and lies between the lower portions of the 

 antero-posterior wing muscles close above the 

 anterior portion of the mid- gut. 



