BEAINS OF THREE GENERA OF ANTS 527 



Figure 14 shows that the anterior dorsal commissure, a.cm., 

 is becoming very slender and is about to disappear, which hap- 

 pens in the next section — not the next figure. In the sections 

 between this and the preceding figure (fig. 13), this commissure 

 served as a path for fibers that come from the inner ocellar lobes, 

 which have now disappeared. In this section (fig. 14), fibers 

 from the outer ocellar lobes, o.oc.L, also pass into the commis- 

 sure. The relation of the ocellar nerve fibers to the protocere- 

 bral commissures will be more fully discussed under the headings 

 of the protocerebral commissures and ocellar nerves. The cen- 

 tral body is still connected by fibers with the protocerebral lobes. 

 The distal ends of the stalks of the mushroom bodies are seen 

 below the central body, divided into two masses, a dorsal and a 

 ventral, the ventral mass labeled p.r. in figure 14, the upper parts 

 of the stalks have disappeared. The approach of the two halves 

 of the brain beneath the esophagus indicates that the subesopha- 

 geal ganglion is about to appear. 



Figure 15 shows the subesophageal ganglion, sb.g, with the 

 mandibular nerves, md.n., issuing from it. The protocerebral 

 lobes merge into the ventral connectives with the subesophageal 

 ganglion, but are still connected with each optic lobe by a slender 

 strand of fibers, and with each other, first, by the fiber tract 

 just above the esophagus, and second, by a commissure which 

 has now appeared, which will be termed in this paper the pos- 

 terior dorsal commissure, p. cm., and which will be described in 

 detail under the heading of the protocerebral commissures. The 

 so-called ''tubercles of the central body," p.r., lie beneath the 

 posterior dorsal commissure. 



Figure 16 is a section through the posterior part of the sub- 

 esophageal ganglion, showing the origin of the labial nerves, Ih.n., 

 the tritocerebral lobes, tr.l., and the tritocerebral nerve, tr.n. 



3. THE PROTOCEREBRAL COMMISSURES 



There are two commissures, or horizontal fiber tracts, present 

 on the dorsal surface of the protocerebral lobes, and connecting 

 the opposite sides. The first, here termed the ''anterior dorsal 

 commissure" begins a short distance anterior to the central body, 

 and continues above and nearly to the end of this body (figs. 12, 



