BRAINS OF THREE GENERA OF ANTS 521 



brain, and the mushroom bodies, m.6., prominent bilobed struc- 

 tures forming the apex of the brain. Each mushroom body con- 

 sists of an outer zone of nerve cells surrounding the calyces, 

 two deeply indented cup-shaped masses of nerve fibers, which, 

 in the whole mounts of the head, appear as two stout crescents. 

 The fibers of the calyces continue downward into the protocere- 

 bral lobes as the stalks of the mushroom bodies, each stalk 

 branching into the anterior root and the posterior root. The 

 paired labro-frontal nerves, Ib.fr.n., which arise each from a 

 single root posterior to the origin of the antennary nerves, soon 

 divide into two branches, the labral nerve, Ib.n., to the labrum, 

 and the frontal nerve, running forward to the frontal gan- 

 glion, fr.g., situated between the bases of the antennae near the 

 anterior surface of the head. Several small nerves, whose course 

 was not determined, run forward from this ganglion; the recur- 

 rent nerve, r.n., also arises in it, but runs backward above the 

 esophagus throughout its length. The second part of the esoph- 

 ageal ganglion, the deutocerebrum, consists of the antennary 

 or olfactory lobes, a.l., ventral extensions of the protocerebral 

 lobes, ending in the nerve trunks going to the antennae. The 

 third part of the supraesophageal ganglion, the tritocerebrum, 

 is hidden by the esophagus and protocerebrum, but its nerve, 

 the tritocerebral nerve, tr.n., may be seen beneath the esophagus 

 going to the inferior dilator muscle of the pharynx. (2) the sub- 

 esophageal ganglion, sb.g., is seen ventral to the supraesophageal 

 mass, and from it arise the paired nerves that supply the mouth 

 parts and the salivary glands. 



COMPARISON OF THE BRAINS OF THE CASTES 



* 1. The queen brain 



a. Camponotus queen: figure 1; text figure 1. The brain of the 

 Camponotus queen is about one-third of the width of the head, 

 and is situated farther away from the dorsal surface or apex of 

 the head than in either the worker or the male, figures 2 and 3. 

 All parts are proportionately large except the mushroom bodies, 

 m.6., these, on the contrary, are relatively small, projecting very 

 little on the dorsal surface of the brain, and lying quite widely 



