204 THE EMBRYOLOGY OF THE HONEY BEE 



The final stages leading to the completion of the heart are shown 

 in figure 83A and B, representing cross sections of the region 



Fig. 83. Transverse sections through the dorsal region of the fourth 

 trunk segment of late embryos, illustrating the final stages in the develop- 

 ment of the heart. A, Stage XIII-XIV; B, XIV, x 600. 



of the heart in the fourth trunk segment of Stages XIII-XIV 

 and XIV. In the first figure (83A), the cardioblasts (CM) form 

 two strips or strands of cells, each situated a short distance laterad 

 of the mid-line, and with their mesial edges directed slightly 

 dorsad. The rudiment of the dorsal diaphragm (DDpJi), consist- 

 ing of a single layer of cells, projects on each side from the 

 lateral border of the cardioblasts. On the right hand side of this 

 figure, a narrow ridge projects out from the cardioblasts, just 

 below the dorsal diaphragm. This is the last vestige of the 

 former union of the cardioblasts and the remainder of the splanch- 

 nopleure. In the next figure (83B) the mesial edges of the cardio- 

 blasts of each side have approached one another until they are 

 on the point of meeting. The former lateral margins of the 

 cardioblasts have meanwhile also moved rapidly mesiad and have 

 been turned about or "tucked under," so that they also are now 

 directed mesiad and almost in contact with one another. In 

 transverse sections therefore the cardioblast strand of each side is 



