530 CAROLINE BURLING THOMPSON 



4. OCELLI, OCELLAR NERVES, OCELLAR LOBES 



Ocelli are present in all three castes of the three genera in 

 question, with the exception of the worker of Camponotus in 

 which they are absent. In the workers of Formica and Lasius 

 the ocelli are much reduced in size. The unpaired ocellus is 

 always anterior to the paired ocelli. The nerve from the unpaired 

 ocellus immediately divides into two branches which run back- 

 ward and downward, meeting the nerves from the paired ocelli 

 just outside the brain sheath (fig. 10). 



The place and mode of entrance into the brain of these ocellar 

 nerves varies in the different castes. The nerves enter farther 

 forward in the queens than in the workers, and still farther back 

 in the males. In the queens and workers the nerves from the 

 anterior ocellus penetrate the brain sheath a short distance in 

 front of the nerves from the posterior ocelli; in the males, all 

 four nerves penetrate the brain at about the same point. The 

 nerves enter the queen brain in a plane about parallel with the 

 anterior surface of the mushroom bodies, and well in front of 

 the central body. In the workers, the median nerves, from the 

 unpaired ocellus, enter the brain above the anterior part of the 

 central body, but the lateral nerves, from the unpaired ocelli, 

 enter the brain behind the central body. The nerves of the males 

 all enter the brain at one point, just posterior to the central body 



After their entrance into the brain the fibers from the four 

 ocellar nerves in all three castes expand into the four ocellar lobes, 

 fiber masses with an outer layer of nerve cells, which lie close 

 together in the median line of the intercerebral region. The ocel- 

 lar lobes of the male and queen are large, those of the worker 

 sniall. The outer lobes, from the paired ocelli, are larger than 

 the inner lobes, from the unpaired ocellus (figs. 11-13, and figs. 

 22-23, ^.o.^., o.o.L). 



As stated before, the fibers from the ocellar lobes reach the 

 fibrous core of the protocerebral lobes in a different manner in 

 the various forms of ants. In the queens of Camponotus and 

 Lasius (fig. 14, o.oc.l.) the fibers go together with the posterior 

 fibers of the anterior dorsal commissure, which lie just beneath 



