572 CAROLINE B. THOMPSON 



p.r.m.h. seen in figures 19, 23, 26, on the ground that these lobes 

 occupy a position similar to that of the ocellar lobes of ants and 

 are in the neighborhood of the entering ocellar nerves. A very 

 careful examination of a large number of sections, however, 

 proved that there is no connection between the ocellar nerves 

 and these adjacent lobes, and that there is direct connection be- 

 tween the mushroom body stalks, the protocerebral lobes, and 

 the lobes in question, which are, as shown in a preceding section, 

 the posterior roots of the mushroom bodies. 



VI. The optic lobes 



The optic lobes are situated on the lateral surfaces of the proto- 

 cerebrum and are present in all the castes of L, flavipes, although 

 they are well developed only in the sexual forms (figs. 8 to 12, 

 O.I.). They are continuous with the protocerebral lobes and 

 consist of an outer layer of very small nerve cells, similar in size 

 to those of the mushroom bodies, and an inner fibrous portion 

 that is subdivided into the outer, middle, and inner fiber masses, 

 and the outer and inner crossings of fibers found in the typical 

 insect brain, Berlese ('09). 



The optic lobes of the nymph with long wing pads are the 

 largest and most highly developed of any caste studied. The 

 outer fiber masses (fig. 17, o.f.) are slender and elongated in a 

 dorso-ventral direction. Nerve fibers pass in to them from the 

 compound eyes, and continue inward, as the outer crossing, to 

 the middle fiber mass, mf., the largest of the three masses. 

 Fibers again cross between the middle and the inner fiber masses, 

 i.f., making the inner crossing. The small inner fiber masses 

 are directly continuous with the fibrous core of the protocerebral 

 lobes. 



In the nymph with short wing pads (fig. 10) the optic lobes 

 and the compound eyes are slightly smaller than in the nymph 

 just described, but the relative size and arrangement of the parts 

 is the same. 



In the worker, although the optic lobes are very much reduced 

 in size, they are readily seen in surface views (fig. 11) as small 



