MUSHROOM BODIES OF BOMBUS 285 



Figure 4 shows the two heavily stippled fiber bundles of each 

 posterior root, p.r., and the lightly stippled masses of fibers de- 

 rived from the central body, c.b.f., some of which are passing down 

 into the protocerebral tissue. The stalks of the mushroom bodies 

 have entirely disappeared except for a shght remnant of the left 

 stalk. 



In figure 5 the fibers derived from the central body, c.b.f., show 

 a further diminution and now exist as two small rounded masses 

 which are connected with each other on the dorsal surface. Fibers 

 are still passing out of these masses into the protocerebral tissue. 

 The two lateral bundles of the posterior roots are fused into one, 

 p.r., situated on each side of the central body fibers, c.b.f., and 

 connected with them by fibers. The proximal ends of the lateral 

 ocellar nerves, l.oc.n., appear in this section. 



In figure 6 the fibers from each posterior root have moved up 

 and fused with a few remaining fibers fron the central body. The 

 fibers of the posterior roots are no longer grouped into small 

 bundles within a larger one, as was shown by the heavier stippling 

 in figures 3, 4, 5, but are spread out at equal distances from each 

 other, and are therefore no longer distinguishable from the fibers 

 derived from the central body. A delicate nerve sheath with 

 small nerve cells on its outer surfaces now surrounds each of these 

 fiber masses, which are here termed the posterior roots, p.r., even 

 though they also contain some fibers from the central body. 



In figures 7 and 8, it may be seen that the two large fiber masses, 

 p.r., or the posterior roots of the mushroom bodies containing also 

 some fibers from the central body, move down nearer to the proto- 

 cerebral core and finally merge into it in a manner similar to 

 that in ants. 



These two large masses of the posterior roots of the mushroom 

 bodies have been frequently termed '^ocellar glomeruli" in the 

 literature of insect brains, on account of their supposed connection 

 with the ocellar nerve fibers. Figures 6, 7 and 8 show that in 

 Bombus as in the ants previously described, there is no connection 

 between the two sets of structures, the ocellar nerves, l.oc.n., mere- 

 ly passing between, never into the posterior roots, p.r. The term 

 ''ocellar glomeruli" is therefore a misnomer for Bombus. 



