1918] Segmentation of Abdomen of Bee 7 



As already stated, the ventral nerve cord of the young bee 

 larva consists, in addition to the suboesophageal ganglion, of 

 eleven single (paired) ganglia, and a terminal ganglion com- 

 posed of three ganglia, the third being much reduced. In 

 mature or nearly mature larvae (4-5 days old) the ventral nerve 

 chain contains only ten single ganglia and one elongate terminal 

 ganglion situated in the 8th abdominal segment instead of the 

 9th, as in young larvas (text Fig. 2). Longitudinal sections 

 through this ganglion show that it is made up of four ganglia, 

 the 8th, 9th and 10th and rudimentary 11th abdominal ganglia 

 (Fig. 4). This ganglion has now a very compact structure, the 

 transverse commissures of the 9th and 10th abdominal segments 

 being brought close together. Sections through younger larvae 

 of different ages show that the incorporation of the 8th abdom- 

 inal ganglion into the compound terminal ganglion takes place 

 slowly, being preceded by a gradual approximation of the 8th 

 and the terminal ganglia extending over almost the entire larval 

 period. As the larva increases in size the 8th and 9th (terminal) 

 abdominal ganglia move up into the 8th abdominal segment, as 

 shown in Figure 3, which represents a section through the last 

 two ganglia of a larva three days old. This cephalad migration 

 indicates a relative shortening of the entire ventral nerve cord, 

 probably caused by the evident failure of the nervous system 

 to keep pace with the rest of the larva in respect to increase in 

 size. The terminal ganglion of an old larva possesses four pairs 

 of lateral nerves, the first two having a common root, innervat- 

 ing the 8th abdominal segment while the other two pairs 

 innervate the 9th and 10th abdominal segments and are refer- 

 able to the ganglia originating in these segments. 



The fusion of the four last ganglia of the ventral nerve cord 

 in the larva evidently foreshadows the imaginal condition, 

 although there is no further union of ganglia during the larval 

 period. The composition of the ventral cord in the young 

 larva, the mature larva and the imago may be expressed in the 

 following formulae, the ganglia of the thoracic segments being 

 indicated by Roman, the abdominal by Arabic numerals, and 

 the ganglia united together to form compound ganglia being 

 enclosed by brackets: 



Newlv hatched larva. . I, II, 111,1, 2, 3, 4, 5, 6, 7, 8, [9, 10. 11]. 



Mature larva I, II, 111,1, 2, 3, 4, 5, 6, 7, [8, 9, 10, 11]. 



Imago (Snodgrass 1910). I, [II, III, 1, 2], 3, 4, 5, [6, 7], [8, 9, 10, 11]. 



