102 



CIRCULATION AND RESPIRATION OP INSECTS. 



being propelled forwards by the successive contractions of its 

 different chambers, it passes out in front by a series of canals, 

 of which some convey it to the head, whilst others pass side- 

 ways and backwards (), for the supply of the body with its 

 appendages, the legs and wings. On returning from these parts, 

 it re-enters the dorsal vessel, partly at its posterior extremity, 

 and partly by the lateral orifices already mentioned. 



619. It will be observed that, in this course, there is no 

 special conveyance of the nutritious fluid, when rendered venous 



Head. 



1st Pair of Legs 



1st Segment of 



Thorax 



Origin of Wing 

 2nd Pair of Legs 

 3rd Pair of Legs 



~ Air-sacs 



FIG. 326. RESPIRATORY APPARATUS OF INSECT (NEi>A). 







in its character by circulating through the tissues, to a particular 



