THE EMBRYOLOGY OF THE HONEY BEE 145 



all of the neuromeres now rising above the internal instead of the 

 external surface of the ectoderm. 



The lateral aspect of the head at Stage X shows little evidence 

 of the two anterior brain neuromeres. Its surface appears hemi- 

 spherical, smooth and unbroken except for the button-like anten- 

 nae. The dorsal aspect of the head however enables one to gain 

 a conception of the general form of the protocerebral lobes at this 

 stage. This is illustrated by Fig. 53, taken from a camera draw- 



ee 



) I I 4-~Mlnt 



Fig. 53. Dorsal view of embryo, Stage XII, showing outlines of proto- 

 cerebrum (iBr), x 112. 



ing. The protocerebral lobes are now seen to be oval in outline, 

 their smaller ends directed backward and outward, their long axis 

 diverging at any angle of about fifty degrees. 



The prismatic cells composing the ectodermal thickening which 

 constitutes the future brain, at Stage VIII are precisely similar 

 to those of the corresponding neurogenic area of the trunk. Dur- 

 ing Stage IX and X the brain rudiment undergoes a differentiation 

 corresponding with that of the ventral cord. Near the inner sur- 

 face of the ectoderm of all three segments of the brain appear the 

 clear and rounded nuclei of neuroblasts (Fig. 54, A and B, Nbl). 

 The future history of these cells appears to be essentially similar 

 to those of the ventral cord, although their study in the brain is 

 much more difficult than in the ventral cord because of the way in 

 which the brain is bent about the anterior end of the egg. Never- 

 theless, in favorable sections the same phenomena may be observed. 

 Figure 54A shows the unequal teloblastic division of a neuroblast 

 in the rudiment of the deutocerebral segment, and also two ad- 



