TuRNER, Mushroom Bodies of the Crayfish. 359 
CONCLUSIONS. 
The purpose of this paper being not so much to make an 
exhaustive study of the brain as to carefully investigate the en- 
vironment of the mushroon-bodies, especial stress has been 
placed upon the fiber tracts related to the mushroon bodies and 
to the intra-cerebral tracts of the cranial nerves, and certain 
tracts not directly related to these have been passed over with- 
out a word. 
Histologically the supra-oesophageal ganglia of the deca- 
pods differ from those of the insects in lacking trache and in 
having the optic lobes separated from the brain; yet the evi- 
dence in favor of their being homologous structures is over- 
whelming. 
The supra-oesophageal ganglion of the crayfish gives origin 
to five pairs of nerves. 
The crayfish brain contains a central-body homolgous to 
the central-body of the insect brain. 
This central body is found, not only in the decapods but 
also in the lower crustacea and even in certain worms. 
Histologically this central-pody is a mass of fine fibrils. 
This central-body receives fibers from several sources, yet 
all the preparations at my disposal militate against VIALLANES’ 
assertion that fibers from this body radiate to all parts of the 
brain. 
Like the insect brain, the supra-oesophageal ganglion of 
the crayfish contains a smaller structure resembling the central- 
body histologically, known as the procerebral bridge. 
The internal structure of the crayfish brain is complicated; 
there are several cell-nidi and each nerve has. related to it 
several fiber-tracts ; but the principal cell-nidi and fiber-tracts 
homologize well with those of the hexapod brain. 
Since the mushroom bodies of the crayfish and insects 
have the same histological structure, since they are situated in 
the same portion of the brain and since they are environed by 
at least five similar bodies, there seems to be no escape from 
