ABBREVIATIONS 



c.b., central body p.d.cm., posterior dorsal commissure 



c.b.f., central body fibers p.r., posterior roots 



c.b.r., central body roots st., stalks of mushroom body 

 r.oc.n., lateral ocellar nerve 



PLATE 1 



EXPLANATION OF FIGURES 



All figures are drawn with the Zeiss camera lucida, Zeiss oc. 2, AA, 150 mm. tube 

 length. Figures 1 to 8 represent consecutive sections through the posterior part 

 of the brain of the worker of Bombus sp. The outer nerve cell layer is blank, the 

 fibrous portions are mottled. 



1 Section through the posterior part of the mushroom bodies, showing the stalks 

 St., connected with the cups, and the posterior part of the central body, c.h. Fibers 

 are seen passing between the central body and the protocerebral lobes, p.L 



2 Section showing fibers in longitudinal section passing from the mushroom 

 bodies stalks into the central body, c.h., and forming the central body roots of the 

 mushroom body, c.h.r. 



3 Section through the posterior end of the central body, c.h., showing its dis- 

 integration into smaller fiber bundles, and also showing the exit of the fibers of 

 the posterior roots, 79. r., from the mushroom body stalks. 



4 Section posterior to the mushroom body stalks, showing four groups of fibers 

 in light stippling derived from the central body, c.h.J., and four lateral groups in 

 heavy stipplings, the posterior roots of the mushroom bodies, p.r. 



5 Shows the continued passage of fibers from the remains of the central body 

 c.h.f., to the protocerebral tissue and the approach of the posterior root fibers, p.r. 

 The proximal part of the lateral ocellar nerves, l.oc.n. is seen. 



6 Shows the fusion of the remaining central body fibers with those of the pos- 

 terior roots, p.r. The beginning of the posterior dorsal commissure is seen on 

 the right. 



7 The two posterior roots, p.r., are moving down toward the protocerebral core. 

 The ocellar nerve fibers, l.oc.n., pass between the posterior roots, and the poste- 

 rior dorsal commissure, p.d.cm., is above them. 



8 The posterior roots, p.r., are merging into the protocerebral core. The origin 

 of the posterior dorsal commissure, p.d.cm., from the protocerebral tissue is seen 

 on the right side. 



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