RESPIRATION IN INSECTS. 



315 



of the blood. Advantage is taken of the facility 

 afforded by the blood-vessels of transmitting the 

 blood to particular organs, where it may con- 

 veniently receive the influence of the air. Thus 

 Scorpions are provided, on each side of the 

 thorax, with four pulmonary cavities, seen at l, 

 on the left side of Fig, 374, into each of which 



air is admitted by a separate external opening. 

 A, B, is the dorsal vessel, which is connected with 

 the pulmonary cavities by means of two sets of 



