148 THE EMBRYOLOGY OF THE HONEY BEE 



Meso 



Ant 



SoeCom 



FIG. 55. Transverse section through head of embryo, Stage XI-XII, 

 showing the formation of the suboesophageal commissure (SoeCom) and 

 the stomatogastric ganglion (StgGng), x 387. 



the brain rudiment (Fig. 55). These clefts then widen out and 

 become occupied by the fibres (Fig. 56). 



While the greater portion of the brain is formed by neuroblasts, 

 parts of both the deuto- and protocerebrum are not formed in this 

 way. These exceptions include the optic lobes, whose develop- 

 ment will be described later, and a pair of small groups of pris- 

 matic cells, situated, when first seen, one on each side, just above 

 the base of the antennal rudiment. These groups of cells become 

 plainly noticeable at Stage XI as a subspherical cluster of large 

 prismatic cells (Figs. 55, and 57, 3;). They apparently do not 

 divide, at least up to the time of the hatching of the larva, but 

 are covered over by the hypodermis derived from the base of the 

 antennal rudiment as shown in figure 57. At Stage XV they 

 are readily recognizable as a spherical group of relatively large 

 cells lying embedded in the deutocerebrum close to its outer sur- 

 face (Fig. 41, y). 



The optic lobes of the insect brain constitute the first, and with 



