BRAINS OF THREE GENERA OF ANTS 549 



fibrous masses and a few ganglion cells situated on the inner sur- 

 faces of the subesophageal ganglion. The fibrous masses (fig. 16, 

 tr.l.), from which the roots arise, project so slightly that they 

 hardly deserve the name of lobes, and yet they represent all that 

 remains of the tritocerebrum. This region is homologous in all 

 castes of the three genera of ants described in this paper. 



It has been stated already that Janet COS), found and described 

 the small nerve which supplies the inferior dilator muscle of the 

 pharynx in Lasius, which "he considered to be the tritocerebral 

 nerve, although he did not trace it to its origin. 



Jonescu ('09), found a similar nerve in the honey bee and suc- 

 ceeded in tracing its origin to two small projections from the 

 subesophageal ganglion which he therefore termed the tritocere- 

 bral lobes. Pietschker ('11, figs. 1-3), shows that the tritocere- 

 bral nerve of C. ligniperdis arises in the same way and in the 

 same position as in the honey bee. 



12. THE SUBESOPHAGEAL GANGLION 



The subesophageal ganglion is united with the protocerebral 

 lobes by the dorso- ventral connectives (fig. 15). This ganglion 

 represents the last three of the six head segments now fused into 

 one mass. From its ventral surface arise the paired nerves of 

 the mouth parts, the very stout mandibular nerves, the maxillary 

 nerves, the labial nerves; from the dorsal surface arise the paired 

 salivary nerves. I have not yet found the paired accessory 

 nerves described by Pietschker, but, as I have given very little 

 attention to this part of the brain, I do not feel prepared to state 

 definitely that they are absent from my preparations. At its 

 posterior end the esophageal ganglion narrows into the ventral 

 nerve cord. 



