GENERAL STRUCTURE. 



39 



horizontal diaphragm or division wall separating the 

 abdomen into two very unequal parts, the larger of 

 which is below. 



This diaphragm"* in contracting increases the upper 

 cavity and diminishes the lower, and so pressing to- 

 gether the viscera, drives from them blood, which 

 now enters the heart chamber or pericardial cavity 

 {pc, Fig. 8), by apertures in the diaphragm itself. 



dv d 



Fig. 8.— Cross Section of Abdomen of Worker Bee (Magnified Eight times). 



dv, Dorsal Vessel ; d, Diaphragm ; pc, Pericardial Cavity ; sp, Spiracle ; tr, 

 Trachea? ; ts, Tracheal Sac ; at, Stomach ; n, Nerve ; c/a, Ganglion. 



The dorsal vessel presents many microscopical 

 curiosities ; it rests upon a cushion of pericardial 

 cells, with singular nuclei, and which sometimes 

 send extensions either into the outer layer of the 

 heart or the diaphragm. We also find here lobes 

 of fatty bodies [corps graisseux), containing here and 

 there the cellules enclavees, or separate cells of 

 Graber, of yellow colour, with a single nucleus, and 

 which resists the action of acids and alkalies, and, 

 beside, multitudes of nerve filaments, and some exceed- 

 ingly fine ramifications of the tracheal system. 



* This diaphragm has been investigated by Graber (see "Archiv fiir 

 Anat. microscop de Schultze," vol. ix., p. 129). 



