INSECTS 



the "blood" ot the insec 

 yellow-tinted lymph. It 



no 



Ao 



Md 



Fig. 69. Diagram of the 

 typical structure of an insect's 

 heart and supporting dia- 

 phragm, with the course of the 

 circulating blood marked by 



arrows 

 Ao, aorta, or anterior tubular 

 part of the heart without 

 lateral openings; Dph, mem- 

 branous diaphragm; Ht, ante- 

 rior three chambers of the 

 heart, which usually extends 

 to the posterior end of the 

 body; Mel, muscles of dia- 

 phragm, the fibers spreading 

 from the body wall to the 

 heart; Ost, ostium, or oneof the 

 lateral openings into the heart 

 chambers 



t, but it is a colorless or slightly 

 is kept in motion, however, by a 

 pulsating vessel, or heart, lying 

 in the dorsal part of the body; 

 and by this means the food, now 

 dissolved in the body liquid, is 

 carried into the spaces between 

 the various organs, where the 

 cells of the latter can have access 

 to it. 



The heart ot the insect is a 

 slender tube suspended along the 

 midline of the back close to the 

 dorsal wall of the body (Fig- 67, 

 Ht). It has intake apertures 

 along its sides (Fig. 69, Ost), and 

 its anterior end opens into the 

 body cavity. It pulsates for- 

 ward, by means of muscle fibers 

 in its walls, thereby sucking the 

 blood in through the lateral 

 openings and discharging it by 

 way of the front exit. An im- 

 perfect circulation of the blood 

 is thus established through the 

 spaces between the organs of the 

 body cavity, sufficient for the 

 purposes of so small an animal as 

 an insect. 



The final act of nutrition comes 

 now when the blood, charged 

 with the nutrient materials ab- 

 sorbed from the digested food 

 in the alimentary canal, brings 

 these materials into contact with 

 the inner tissues. The tissue 

 cells, by the inherent power of 



[112] 



