124 THE EMBRYOLOGY OF THE HONEY BEE 



but diminishes rapidly in calibre as it passes caudad. At a point 

 slightly cephalad of the junction of the oesophagus and the mid- 

 intestine the recurrent nerve divides to form two small and rela- 

 tively insignificant ganglia, the pharyngeal ganglia (Figs. 39 and 

 46, PhyGng). These are flat and lie closely applied to the lateral 

 faces of the oesophagus. 



The corpora allata (Figs. 39, and 42, Cor All) are two conspicu- 

 ous spherical masses of cells which most resemble ganglion cells, 

 but lack nerve fibres. These bodies lie some distance apart in the 

 posterior part of the cavity of the head, just below the level of 

 the lower edge of the oesophagus. These bodies are attached 

 dorsally to the thin walled sacs which constitute the coelomic 

 sacs of the antennal segment. 



2. Development 



Before entering upon a description of the development of the 

 nervous system of the honey bee it will be profitable and in fact 

 almost necessary first briefly to describe the course of develop- 

 ment of the nervous system in the Orthoptera, a relatively primi- 

 tive group, in which the intimate details of the process reveal 

 themselves sharply and distinctly. The broader features of the 

 development of the nervous system in the honey bee are simple 

 and readily understood; the minuter details of the origin of the 

 development of the nervous system, in other words its histogenesis, 

 is on the other hand much more difficult to follow and relatively 

 obscure, in fact so much so that it would be decidedly difficult of 

 interpretation without the assistance afforded by previous work 

 on this subject. 



The nervous system of the insect arises, as was first shown by 

 Hatschek (1877), from two longitudinal thickenings or ridges 

 extending along the ventral side of the germ band, one on each 

 side of the mid-line. These ridges, the neural ridges (Fig. 47, 

 NIR) enclose betwen them a narrow median groove, the neural' 

 groove (NIG), the internal infolded portion of which forms the 

 median cord. From the intrasegmental portion of the median 

 cord and the -neural ridges the ganglia are formed by a process 

 of splitting off or delamination, the outer portion of the ectoderm 

 remaining as the ventral hypodermis; in the interganglionic re- 



