108 



THE ANATOMY OF THE HONEY BEE. 



maintaining the circulation of the blood. " The heart (fig. 1, Ht) is 

 located in the dorsal sinus, which latter is therefore often called the 

 pericardial chamber. The pulsations of the diaphragms are produced 

 by fine muscle fibers lying in their walls. These are usually ar- 

 ranged in a number of fan-shaped bunches on each side radiating 

 from the edges of the diaphragm (fig. 47, DphMcl) toward the mid- 

 dle, where most of them are continuous with the fibers from the oppo- 

 site side. It used to be supposed that those of the dorsal diaphragm 

 produced the expansion of the heart, and they were for this reason 

 called the " wing muscles of the heart," but the latter organ is now 

 known to be a muscular tube and to contract and expand by its own 



FiQ. 47. — Dorsal diaphragm of drone, from one segment and adjoining parts of two 

 neighboring segments, showing median heart {Ht) as seen through transparent dia- 

 phragm (DDph), fan-shaped bunches of diaphragm muscles (DphMcl), and lateral 

 tracheal sac (TraSc) giving off sac-bearing trunks into pericardial chamber above 

 diaphragm. 



power. In some insects the muscles of the dorsal diaphragm form a 

 meshwork of fine fibers surrounding numerous large and small holes 

 in the membrane, which probably permit the entrance of blood into 

 the sinus above, but in most species the diaphragm is imperforate 

 and the blood enters the pericardial chamber above its scalloped edges 

 (figs. 1 and 47) . 



The heart of insects in general is a long narrow tube (fig. 1, Ht) 

 situated in the dorsal sinus or pericardial chamber of the abdomen 

 along the midline of the body. It is swollen toward the middle of 

 each segment into a heart chamber (ht) which presents a vertical 

 slitlike opening or ostium (Ost) on each side. Theoretically^ in 



