370 The American Naturalist. [May, 
Earlier authors, from the time of the first good description of 
the finer structure of the optic lobes by Berger, to Carriére and 
Viallanes, evidently did not understand the significance of this 
outer fibrillar mass. Berger and Carrière considered it as form- 
ing a portion of the retina, and Viallanes found in it, in the 
case of the dragon-fly, structures that he denominated neuro- 
matidia—structures unrecognizable in the bee, and really with- 
out existence in any of the arthropoda. The earlier de- 
scription given by Hickson much more nearly approaches the 
truth, but this author erred in supposing what he saw to be` 
protoplasmic reticuli. The first correct understanding of this 
body was arrived at by Parker, in his application of methylene 
-blue to Astacus. But between the crustacea, as noted by Parker, 
and the hexapoda, there are certain differences of detail that 
are readily apparent upon a comparison of the figure accom- 
panying this paper and that given by the author mentioned. 
Somewhat inside of this mass is the first or outer chiasma 
(x)—to be distinguished as such only in horizontal sections. 
Concerning the two inner fibrillar masses it is to be noted that 
each is composed of two lenticular finally granular, or better, 
in the light of the new neurology, finely fibrillated masses 
separated by a loose mass of fibers that never assume so dark 
an appearance in the ordinary stains. Each body would, if it 
were a perfect segment of a sphere, form a meniscus lenticular 
mass whose convex surface is directed outward. 
From the middle or second fibrillar body two tracts of fibers 
pass into the central cerebral mass as noted in my earlier paper. 
Each arises from the inter-lenticular mass of loose fibers and 
emerges at nearly the same spot with its fellow on the anterior 
side of the body. One passes inward and upward, becoming 
what I have called the antero-superior optic tract, which finally 
terminates among the dendritic fibrils of the cells of the adja- 
cent mushroom bodies (a-s o. ¢.). The fibers of this tract origi- 
nate, as has previously been pointed out, from a group of cells 
lying above the optic body (op. b) and below the anterior surface 
of the calyx of the outer mushroom body. 
The cells and their processes passing inward towards the 
stalks of the mushroom bodies can be readily distinguished in 
