72 



THE STUDY OF INSECTS. 



is usually termed the heart. This is a somewhat complicated organ 



consisting of several chambers arranged in 

 series, and each communicating with the 

 one in front of it by an opening fur- 

 nished with valves. The number and form 

 of these chambers differ in different in- 

 sects. Fig. 82 represents the heart of a 

 May - beetle. These chambers not only 

 communicate with each other, but com- 

 municate with the body-cavity by means 

 of side openings, which are also furnished 

 with valves. These two sets of valves act 

 in such a way that when a chamber of the 

 heart contracts a stream of blood is forced 

 towards the head, and when it expands the 

 blood rushes into it through the side open- 

 ings, and from the chamber behind it. At- 

 tached to the lower surface of the heart 

 and extending out to the side of the body 

 there is on each side a series of triangular 

 muscles : these have been termed the wings 

 of the heart (Plate II, 6, and Fig. 83, c). 

 In Figure c they are represented cut away 



valves ; c ventral aspect of f rom t h e caudal part of the heart. The 



heart and wing-muscles— the 



muscles are represented as prolongation of the heart, which extends 



cut away from the caudal , , . , , . , , , 



part of the heart; d, dorsal through the thorax and into the head, is 



aspect of heart. termed the <wrte. 



The blood is forced by the heart through the aorta into the head, 

 where it escapes into the body cavity. From this point it flows 

 through the body cavity in regular streams, which have definite di- 

 rections, but which are not included in vessels. They, like the ocean 

 currents, are definite streams with liquid shores. 



The blood is usually colorless, or slightly tinged with green; but 

 its circulation is made conspicuous by the movements of the large 

 corpuscles with which it abounds. In transparent insects it can be 

 seen pouring forth from the cephalic end of the aorta, bathing first 

 the brain, and then passing to all parts of the body, even out into the 

 appendages. By tracing the course of any one of these currents it 

 will be found to flow, sooner or later, to the cavity between the wings 

 of the heart and the back in which the heart rests, and from which it 

 receives its blood. 



The Nervous System. — The central part of the nervous system, as 



Fig. 83.— Heart of May-beetle 

 (after Straus-Durckheim): a, 

 lateral aspect of aorta ; b. 

 interior of heart showing: 



