56 
CHAPTER IX. 
BLOOD CIRCULATION. 
Circulating System — Dorsal Vessel — Ventricles — Grader’s Dis- 
covery — Perica7'dial Diaphragm — Pericardial Cavity — Blood 
of the Bee — Speed of Circulation alters zvith Temperature 
— Heat of Blood — Teinperature of Cluster coimected with 
Activity of Respiration — Experiments on Winter Te7npera- 
ture of Cluster — Te^nperature at Different Seasons. 
Bees, like all other insects, have organs of circulation, 
although they have no regular system of blood-vessels 
like the higher animals. Although Swammerdam, 
Malpighi, and Lyonnet had an idea of the method of 
circulation in insects, it was not until Newport (i 19, 120) 
explained the matter that a proper knowledge of the 
process was arrived at, and the still more recent dis- 
coveries of Graber (51, 52, 53), in themselves of the 
highest importance, have cleared up what was un- 
certain and for so long a time contested. 
The dorsal vessel (Fig. 27), which is a heart con- 
taining a series of cavities, or ventricles^ is situated 
immediately under the external covering of the back 
of the insect, and extends from near the end of 
the abdomen, where it is closed, to the head above 
the oesophagus, where the tube is open near the 
brain. 
The walls of the heart are made up of three layers, 
a thin inner lining (the endocardium) attached to a 
central striated muscular wall, and an outer coat of 
connective tissue {pericardium). In the queen and 
