470 



ARTHROPODA. 



Since the tracheae, with their fine branches, supply the tissues 

 directly with oxygen, the blood-vascular system is rudimentary. 

 Directly under the back lies the elongate tubular heart in a special 



FIG. 494. 



FIG. 495. 



FIG. 494. Anatomy of honey bee. (From Lang, after Leuckart.) ", antennae: au, 

 eye ; 6, legs; cm, chyle stomach; ed, rectum ; hm, honey stomach iproventriculus) , 

 rd, rectal glands; s, spiracles ; tb, tracheal chambers with tracheae ; v/n, Mal- 

 pighian tubules. 



FIG. 495. Abdomen of Ephemera larva (from Gegenbaur) with tracheal gills, c; a, 

 tracheal trunks ; b, intestine ; d, caudal bristles (cerci). 



pericardial sinus. This is a part of the haemoccele cut off from 

 the gastric portion of this space by an incomplete partition in 

 which, right and left, are the wing muscles (alee cordis) of the 

 heart. The heart receives its blood through lateral ostia (eight or 

 fewer) from the pericardial sinus or (Orthoptera) through ventral 

 openings from the large haemocoele. The blood passes forward 

 through an anterior aorta into the haemocoele and thence back to 

 the pericardial sinus. The arrangement of the viscera, fat bodies, 

 and muscles gives a certain regularity to the circulation, especially 

 in the appendages. Accessory pulsating ampullae in the bases of 



