THE EMBRYOLOGY OF THE HONEY BEE 135 



The final changes leading to the functional larval ganglion are 

 illustrated by figure 5oD, Stage XIV. The most important 

 changes are: the development of nerve fibres, the development 

 of the lateral nerves, and the final incorporation into the ganglia 

 of the intraganglionic portions of the median cord. 



The development of the nerve fibres corresponds essentially to 

 the accounts of Wheeler (1893) an d Heymons (1895). The 

 ganglion cells of both the median and the lateral cords at about 

 Stage XII become pyriform; the smaller pointed ends of the 

 ganglion cells of the lateral cords being directed toward the clefts 

 already described, while the smaller ends of the cells of the median 

 cord are directed more or less dorsad. The smaller ends of the 

 ganglion cells now become more and more attenuated and finally 

 elongate into delicate protoplasmic fibres, the nerve fibres. Dur- 

 ing this process, in those regions where the commissures are 

 formed, a vacant space also appears in the dorsal half of the 

 median cord, in line with the spaces in the lateral cords, with 

 which it unites. These spaces are traversed from side to side 

 by the cell processes which are to constitute the nerve fibres of 

 the transverse commissures (Fig. 5oD, NvF). These commis- 

 sural nerve fibres appear to arise from both the cells of the 

 median and lateral cords, but mainly from pyramidal groups of 

 cells situated immediately laterad of the median cord (see also 



Fig- 3?A). 



The lateral nerves are apparently formed from the aggregations 

 of ganglion cells which at Stage XI-XII (Fig. 506) constitute 

 the extreme lateral portions of the ganglionic rudiments. These 

 lateral cell groups are presumably derived by migration of gan- 

 glion cells which formerly lay within the semicircle formed on 

 each side by the neuroblasts, since there is no evidence that cells 

 are ever budded off from the neuroblasts in a laterad direction. 

 Moreover both the arrangement of these lateral cells, and the 

 fact that the number of ganglion cells lying immediately dorsad 

 to the neuroblasts is perceptibly diminished when the lateral 

 cell groups appear, tend to confirm this conclusion. The fate 

 of the lateral cell masses is clearest in the gnathal segments, since 

 in these the lateral nerves are short and straight, so that the entire 

 nerve together with the ganglion from which it arises may be 



