n6 THE EMBRYOLOGY OF THE HONEY BEE 



...OpPI 



FIG. 38. Diagram of the nervous system of an embryo of Mant 

 showing the head and first three trunk segments. iFrom Viallanes. 



includes the greater portion of the brain and is made up of a pair 

 of large lobes (Figs. 39-44, iBr) situated in the upper part of 

 the head capsule. These lobes are somewhat ovoid in form, their 

 larger ends directed caudad and slightly laterad; their smaller 

 anterior ends lie close to the anterior wall of the head. Each 

 lobe is somewhat compressed at right angles to the external sur- 

 face. At their anterior ends the lobes are closely apposed to 

 each other and are here united by a thin bridge of nerve fibres, the 

 supraoesophageal commissure (Figs. 43 and 44, SupCom). Prob- 

 ably some fibres from the second brain division, the deutocere- 

 brum, also enter into this commissure. 



Each half of the protocerebrum of insects is typically divided 

 into three lobes, which in many cases, as in the Dermaptera and 

 Orthoptera (Fig. 38) are marked off from one another by thick- 

 enings of the ectoderm forming the wall of the head capsule. 



