iS8 THE EMBRYOLOGY OF THE HONEY BEE 



of this system first make their appearance at Stage IX, but are 

 more sharply marked at Stage X. At this stage three evaginations 

 of the dorsal wall of the stomodeaum wall are visible (Fig. 60). 



FtGnr 



■ Meso 



Fig. 60. Median sagittal section through the stomodaeum of an embryo, 

 Stage X, showing the three evaginations of the dorsal wall of the stomo- 

 daeum which form the stomatogastric system, x 387. 



On the lower surface of this wall these appear as sharply pointed 

 clefts, on the upper surface as rounded swellings (Fig. 55, FtGng). 

 The first (anteriormost) of these is relatively insignificant, while 

 the other two are very noticeable. The first is situated not far 

 from the end of the labrum, the second close behind the first, 

 while the third is halfway between the second and the point where 

 the oesophagus joins the mid-intestine. The first evagination lib- 

 erates a few scattered ganglion cells which later are found ac- 

 companying the labral nerve, and then quickly disappears. The 

 second forms a large ovoid mass of nerve cells lying just above 

 the oesophagus and between the two halves of the brain, and is 

 easily recognized as the frontal ganglion (Fig. 5,5, FtGng). This 

 mass is at first hollow, with the cavity of the evagination extend- 

 ing up through it, but soon becomes solid. The third mass of 



