110 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
which Krieger (’79) designates as gz;. In my own preparations of the 
brain of the crayfish I find that this ganglion resembles the “ ganglion 
antennaire” of Annelids in the following points. In both, (1) such 
ganglia are confined to the brain, no similar structure occurring in the 
ventral cord. (2) The ganglion is intimately associated with the masses 
of neuropil, which also occur nowhere but in the brain. (3) The small 
size of the nuclei and the meagre cytoplasm distinguish these cells 
from the other cells of the brain. (4) There is a peculiar arrangement 
of the cells in rows radiating from the neuropil. According to the de- 
scription given by Kenyon (’96), the mushroom bodies of the honey bee 
exhibit the same peculiarities. The chief difference to be found in the 
three cases is the relative size of the nuclear and the neuropil masses, 
and in the arrangement of the two parts. In Nereis the nuclear mass 
partially surrounds the neuropil, whereas in the insect the relation of 
the two parts is reversed, the neuropil partly enveloping the nuclear 
mass. The crayfish presents an intermediate condition in this respect, 
The nuclear elements do not stain readily in methylen blue, —a condi- 
tion also found by Allen and Bethe in Crustacea, and by Retzius in 
Nereis ; but in the bee Kenyon obtained impregnations of the cells by 
the Golgi method. His preparations show that the cells of these ganglia 
send processes into the neuroglia, where they end in dendrites almost as 
complex as those found in the brain of Vertebrates. Since in the worm 
there is relatively little neuropil, the dendrites of the associated cells 
will probably be found to be less well developed. Kenyon’s supposition 
that the intelligence of the insect is to be accounted for by the com- 
plexity of the relations between the nervous elements made possible by 
these association fibres seems quite plausible ; and if we apply the 
same argument to the worm, we may suppose its low intelligence to be 
in part correlated with the small amount of neuropil, or, in other words, 
the limited development of the association fibres. 
Aside from the cells of this ganglion and those connected with the 
ciliated groove, the brain of Nereis contains about as many cells as a 
typical ganglion of the ventral chain. If we compare the brain with 
the ganglia of the ventral chain, or if we compare the central nervous 
system of Annelids with that of Arthropods, the only structural condi- 
tion to be found which warrants the supposition that it is correlated 
with the supposed psychic functions of the brain is the mushroom body 
and the related development of association fibres. This correlation has 
often been pointed out for insects, and I think we may extend the ob- 
servation to decapod Crustacea and Annelids. 
