TuRNER, WVushroom Bodies of the Crayfish. 357 
nuclei and almost no cytoplasm. In this respect they resemble 
DEITER’s corpuscles of the vertebrate brain. Compact masses 
of these cells crown stalks of nerve fibers and remind one of 
miniature mushrooms. In these nidi the cells are arranged in 
rows which radiate from the top of each stalk. In many insects 
each nidus is lodged ina cup-shaped structure known asa 
calyx. A cup-shaped calyx, however, is not a constant com- 
ponent of the mushroom bodies even in insects. KENYON has 
written (96): ‘‘The bodies [calyx of the mushroom bodies] 
reach their highest development in the Hymenoptera and are 
much larger in the social wasps than in the honey bee. In 
Blatta the lateral walls of the cups are much reduced, and in 
the Coleoptera the cup-like form is scarcely, recognizable, while 
in forficula and Acridum the fibrillar substance only forms a 
broad plate. Even this is scarcely, if at all, recognizable in 
Dytiscus. In Tabanus and Somomya the four folds are reduced 
to two and in the former of these genera are scarcely to be dis- 
tinguished by a comparison of their cells with those surround- 
ing them.” 
Stalks of the Mushroom-bodtes. 
In the crayfish each mushroom nidus rests upon a tract of 
nerve fibers, bearing towards the tract the same relation 
that the pileus does to the stalk of the mushroom. The nidus 
surmounted tracts are known as the stalks of the mushroom 
bodies. Inthe crayfish these stalks of the same half of the 
brain converge and unite (figs. 22, 25). This is also the case in 
many insects, as may be seen by examining the brain of a larval 
butterfly (fig. 26) or by consulting KENnyon’s work on the bee. 
These peculiar mushroom nidi with their stalks are found not 
only in the crayfish but also in certain worms: i. e. (Verets (fig. 
28), Polynée (fig. 29), Lepidonotus (fig. 30). In these worms, 
however, instead of having two distinct mushroom nidi on each 
side, we find only one, or else one partly divided. 
Roots of the Mushroom-bodies. From the point of union 
of the stalks of the mushroom-bodies arise two fiber tracts 
known as the stalks of the mushroom bodies. The more me- 
