TuRNER, Mushroom Bodies of the Crayfish. 325 
3. The nerve fibers occur in the peripheral nerves, the 
transverse commissures and longitudinal columns. 
4. Each nerve fiber is provided with a sheath, which, in 
large tubes, is double. 
5. The contents of the nerve tube is semi-viscous, clear 
and homogeneous. 
6. The nerve cells which occur in all ganglia are of the 
following shapes: oval, pyriform, fusiform. In structure they 
resemble the cells of the sympathetic ganglia of vertebrates. 
7. The cells are usually superficial. 
8. Each ganglion contains three commissures. 
g. There is no central body; what is considered such by 
authors is a collection of three transverse commissures. 
10. The ganglia of the brains of Brachyura and Macroura 
are morphologically similar to each other and to the insect 
brain. 
W. Viena (’83) after giving an exhaustive historical 
résumé discusses the nervous systems of the Crustacea, Hiru- 
dinians, Oligochztes, and Mollusca. The following conclusions 
concerning the nervous system of the Crustacea were the fruits 
of his investigations of the following types: lobster, rock-lob- 
ster, Palemon, crayfish and crab. 
1. The membrane of the large nerve tubes has a double 
contour while that of the smaller a single. Otherwise they are 
similar. 
The majority of the cells are unipolar, some are bipolar, 
still fewer are multipolar; but none are apolar. He could not 
detect the concentric arrangement of granular fibrils around the 
nucleus which Remax describes. 
3. The cells of the cerebrum, thorax and abdomen are 
chiefly unipolar. 
4. The nerve chain is surrounded by two envelopes. 
5. The two halves of the chain are united by commis- 
sural fibers and numerous cells. 
6. The nerve cells on the ventral side of a ganglion send 
their processes into the center of the same. 
