THE ORGANS OF CIRCULATION AND RESPIRATION. 



139 



true. They do not pass into the heart at all. Even if they did, 

 a pull from opposite sides upon a flexible, cylindrical tube, 

 would narrow and not expand its cavity. Moreover, direct 

 observation* shows that the heart continues to beat after all the 

 alary muscles have been divided, and even after it has been cut 

 in pieces. These facts suggest that the heart of Insects is in- 

 nervated by ganglia upon or within it, and indeed transparent 

 larva), such as Corethra or Chironomus, exhibit paired cells, 

 very like simple ganglia, along the sides of the heart. 



Ht 



Fig. 76. Heart and Pericardial Diaphragm. On the right, as seen from above ; on 

 the left, as seen from below ; the bottom figure represents a transverse section. 

 Ht, heart ; PD, pericardial diaphragm ; A M, alary muscle ; Tr, trachea! tube ; 

 PC, pericardia! fat-cells ; PC 1 , niultinucleate fat-cells. 



Scattered over the upper surface of the pericardial diaphragm 

 are groups of cells, similar to the fat-masses of the perivisceral 

 space. Over the fan-like expansions of the alary muscles are 



* Brandt, Ueb. d. Herz cler Insekten u. Muscheln. Mel. BioL Bull. Acad. St. 

 Petersb. Tom. YI. (1866). 



