350 JOURNAL OF COMPARATIVE NEUROLOGY. 
body. In the crayfish brain I have not been able to trace any 
fibers from the procerebral bridge to the central body; but 
numerous fibers arise in the dorsal nidus (which lies just above 
the procerebral bridge) and pass around the procerebral bridge 
to the central body and to the commissure which lies just above 
the central body. If these fibers give off branches to the pro- 
cerebral bridge I have not been able to detect them. 
Although the central body is present in Bvanchipus, yet 
my sections reveal no trace of the procerebral bridge; but since 
in that case one section contains the whole of the central body, 
the much smaller procerebral bridge raight have been destroyed 
by the microtome knife. It would not be wise then to conclude 
that there is no procerebral bridge in Branchipus. 
Most of my sections of worms reveal nothing that I would 
feel justified in calling a procerebral bridge; but in transverse 
sections of Lepzdonotus I find a structure (fig. 30, P..) which 
may be the homologue of the procerebral bridge. In Lepz- 
donotus this structure is composed of a meshwork of fibers which 
reacts towards stains in the same manner as the fibers of the 
procerebral bridge of the crayfish. Near it is a cluster of cells 
which may correspond to the dorsal nidus of the crayfish brain. 
Olfactory Lobe (figs. 1-9, 14, 20, 25, Ol.L.) The olfac- 
tory lobes are located one in the dorsal portion of each half of 
the brain, between the outer and inner mushroom nidi. Each 
lobe is nearly spherical in shape and is about five millimeters 
in diameter. Histologically, the body is composed of three 
parts: Ist, a central core of fibers (fig. 5, a); 2nd, a region 
composed of fine fibrils arranged in dense subconical masses 
which radiate from the central core (fig. 5, 0); 3rd, an outer 
layer of fibers (fig. 5, ¢). 
Optic Lobe (fig. 1-9, 11-14, 20-23, 25, Op.L.). The optic 
lobes are located one in the ventral portion of each half of the 
brain, between the mushroom nidi and the latero-ventral nidus. 
They are ellipsoidal in shape and are much larger than the olfac- 
tory lobes. Histologically the body is composed of numerous fine 
fibrils grouped in such a manner as to cause sections of the body 
to have a mottled appearance. In the center of the dorsal lobe 
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