THE EMBRYOLOGY OF THE HONEY BEE 195 



body cavity, except in the intersegmental regions, where it extends 

 laterad to the hypodermis, to which it is attached (Fig. 76, 



Fig. 76. Transverse section through the dorsal region of the trunk, 

 between the 5th and 6th trunk segments, showing the attachment of the 

 dorsal diaphragm (DDph) to the hypodermis, x 600. 



DDph). This relation is clearest in the third to the ninth trunk 

 segments inclusive, but undoubtedly also exists in the first two 

 (thoracic), although masked here by the crowded condition of the 

 parts and the large number of pericardial fat cells. The muscle 

 fibres constituting the dorsal diaphragm of most insects, includ- 

 ing the honey bee (imago), are commonly described as radiating 

 fanwise from the points of origin to their attachment on the 

 heart {vide Snodgrass, 1910, p. 108), but in the young larvae no 

 muscle fibres could be seen in the dorsal diaphragm, which appears 

 in both longitudinal and tranverse sections as a continuous and 

 extremely thin membrane. 



The cells constituting the dorsal diaphragm are of two kinds ; 

 numerous flat cells with minute nuclei (Fig. 70), appearing to be 

 the diaphragm cells proper, and pale lenticular cells whose size 

 approximates that of the fat cells (Fig. 76 ParC). An examina- 

 tion of the text and figures of Carriere and Burger's (1897) 

 account of the dorsal diaphragm of Chalicodoma makes it evident 

 that the cells just described are identical with those constituting 

 the "paracardial cellular cord" (paracardial Zellstrang). This 

 term was first used by Heymons (1895) to designate segmentally 



