150 THE EMBRYOLOGY OF THE HONEY BEE 



2Br 



Hyp...- 



FIG. 57. Part of a transverse section of Stage XI -XII, passing through 

 the antennal rudiment (Ant), showing one of the pair of spherical cell 

 groups of unknown significance (Y), which enter the deutocerebrum 

 , x 600. 



future optic lobes. Here the regular palisade-like arrangement 

 characteristic of the neurogenic epithelium at earlier stages is 

 preserved, the rudiment of the optic lobes appearing as a thick 

 epithelial plate composed of slender prismatic cells with large 

 nuclei (Fig. 58 A, OpL). Only a limited number of neuroblasts 

 are produced from this area. These, together with the progeny 

 of adjacent neuroblasts form a mass of cells underlying all but 

 the extreme lateral borders of the epithelial plate. On its ex- 

 ternal rounded margin the epithelial plate is sharply demarcated 

 from the dematogenic ectoderm immediately adjacent, which 

 equals the epithelial plate in thickness and is composed of narrow 

 prismatic cells of the smaller size characteristic of the dermato- 

 genic ^ectoderm (Fig. 58A, OpPl). This dermatogenic layer be- 

 comes thin at its edge* 1 where it meets the optic lobes, the thin 

 edge overlapping and covering their margins. 



The epithelial plate destined to form the optic lobes is at Stages 



