358 JouRNAL OF COMPARATIVE NEUROLOGY. 
dian of these, which is the narrower, passes inward (mesad) un- 
til past the border of the lobe in which it lies; then it turns meso- 
dorsad until it nearly abuts against its fellow from the opposite 
side; then the two pass side by side for a short distance and 
then diverging pass into the optic nerve. The other tract passes 
outward and loses itself among the fibrils of the optic lobe. 
These stalks are found not only in the crayfish (fig. 7), but 
also in the insects (fig. 26) and worms (fig. 28). 
Minute Structure of the Mushroom Nidt. The cells of this 
region are peculiar in containing little or no extra-nuclear pro- 
toplasm. Fibers from these cells pass into the optic lobe and, 
branching dendritically, give it a speckled appearance. 
It is thought that the comparative value of the facts dis- 
cussed above can be best appreciated by consulting the follow- 
ing table: 
COMPARISON OF THE MUSHROOM BODIES OF INSECTS, CRAYFISH 
AND WORMS. 
Crayfish Insects Worms 
Located in the supra-ocsopha-| Located in the supra-oesopha-|Located in the supra oeso- 
geal ganglion geal ganglion phageal ganglion 
Four nidi of cells Four nidi of cells (sometimes}Two nidi of cells (some- 
only two) times each nidus is par- 
tially subdivided) 
Cells of each nidus arranged in 
rows which radiate from a 
common base 
Cells contain little or no extra- 
nuclear protoplasm 
Cells of each nidus arranged in|Cells of each nidus ar- 
rows which radiate from ajranged in rows which radi- 
common base ate from a common base 
Cells contain little or no extra-/Cells contain little or no 
nuclear protoplasm extra-nuclear protoplasm 
Fibers from the ce!ls branch 
dendritically giving the brain 
near the cells a speckled ap- 
pearance 
Each nidus caps a stalk of, 
nerve fibers 
Fibers from the cells branch 
dendritically giving the brain 
near the cells a speckled ap- 
pearance 
Each nidus caps a stalk of|/Each nidus capsa stalk of 
nerve fibers nerve fibers 
In the neighborhood we find: 
Central body. 
Procerebral bridge, 
Lower optic commissure, 
Optie chiasm, 
Fibrillar arch, 
Ete. 
In the neighborhood we find; 
Central body, 
Procerebral bridge, 
Lower optic commissure, 
Optic chiasm, 
Fibrillar arch, 
Etc. 
In the neighborhood we 
find: 
Central body 
