20 



INSECT TRANSFORMATION 



the upper pair run on either side of the long tubular heart 

 (Fig. 10 h). This important organ extends in insects along the 

 central axis of the body just below the dorsal wall, lying in a 

 shallow chamber (pericardial blood-space) (Fig. 10 pc) bounded 

 above by that wall and beneath by a delicate, perforated mem- 



a.s 



U sp. 



a.s 



FIG. IO. DIAGRAM OF HEART (h) AND PART OF AIR-TUBE 

 (TRACHEAL) SYSTEM OF A LOCUST. 



ao, aorta ; pc, pericardial space ; sp, spiracles ; as, air-sacs. 

 X2. In part after Emerton (Packard's "Text-book.") 



brane which roofs in the main cavity of the body. After being 

 propelled along the heart, by rhythmic contraction of its 

 muscular wall, from behind forwards, and then through tubular 

 vessels (arteries), the blood passes into this main cavity. This 

 arrangement of the blood-system affords a marked contrast 



