Figure 2.
Bee brain structure. Ai, The bumblebee brain. Aii, A horizontal section of the bee brain stained with osmium taken from the level of the dashed lines in Ai. Specific areas of the optic lobe subdivisions are indicated: the retina (ret), the lamina (la), the medulla (me), and the lobula (lo), as well as the central protocerebrum (prot). B, Bombus impatiens lobula structure. Reduced silver Bodian staining, six layers can be seen within the lobula, which progress from the outer portion of the lobula (i.e., layers 1–3) to the inner, or proximal, regions of the lobula (i.e., layers 4–6). The distal layers (1–4) contain a spatially ordered arrangement interspersed with horizontal branching. In addition, larger processes dominate layer 4. The arrangement breaks down in layers 5 and 6, where the large processes form a complex network. C, Input to the lobula, which follow the internal structure of the layers (site of dye injection at the asterisk). D, In this mass fill of medullar neurons, the input to the lobula is clearly columnar in the outer, or distal, regions of the lobula, which disappears in the inner layers 5 and 6. E, Multiple sections of the brain can be used to reconstruct a three-dimensional representation of the brain, with the optic lobes (lo and me), the antennal lobes (al), the central complex (cc), and the mushroom bodies (mb). F–H, The lobula and the component layers were three-dimensionally reconstructed from individual sections (F) using a custom Matlab program. G is the same view as in A–D, whereas H is a rotated view. Note how the outer layers (1 and 4) form rinds around the inner layers (5 and 6). We also reconstructed the tracts leaving different regions of the lobula (gray, orange, green, yellow, red, and purple tracts). aott, Anterior optic tubercle tract.