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 
^UfterStrawOurelScSn^ 1 ', of the heart. (Plate II, 6, and Fig. 83. c). 
tateriir“ P f' C heart "showing In Fi g ure * the y are represented cut away 
valves ; c. ventral aspect of f rom the caudal part of the heart. The 
heart and wing-muscles— the . , ,. . , 
muscles are represented as prolongation of the heart, which extends 
part^^eheart 1 ;^ dorsal through the thorax and into the head, is 
aspect of heart. termed the aorta. 
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 
