STUDIES ON THE NERVOUS SYSTEM OF CRUSTACEA. 489 
nerve bifurcate in the cesophageal ganglion, a branch then 
passing into each of the ventral nerves (figs. 1 and 3, H). It 
is probable that in this way the commissural ganglia are 
placed in direct communication with the brain. As, however, 
I have not followed one of these fibres individually to the com- 
missural ganglion, there is of course the alternative that it 
may pass out at the brauch (0) and enter the plexus (plez.) 
at the border of the mouth. 
Passing now to the dorsal nerves (dors. n.) arising from the 
commissural ganglia, I was here again able to complete the 
observations I had made on Astacus by those on the lobster 
embryos. In the latter, fibres were often observed starting 
from cells in the commissural ganglia (fig. 2, B), and after 
giving off numerous arborescent collateral branches to the 
neuropile, passing into the dorsal nerve and so to the 
azygos. 
After leaving the commissural ganglion, the dorsal nerve 
gives off a branch (d) which runs upwards on the wall of the 
cesophagus and soon breaks up into a large number of in- 
dividual fibres, each one having in its course a moderately 
large bipolar cell (3, fig. 1). These cells exactly resemble 
sensory cells described by Retzius! in many Polychetes and 
Molluscs. 
As near as I could determine in preparations in which the 
general tissue was not stained, they lie on the exterior surface 
of the cesophagus, whilst the distal fibres proceeding from the 
cells, sometimes after a very long course, end in a much deeper 
layer, probably on the interior face of the esophagus. The 
proximal fibres from these cells all enter the branch (d) of 
the dorsal nerve, and the fibres of this branch enter the com- 
missural ganglion. 
A few fibres passing through the branch (d) break up on the 
1 Retzius, ‘ Biol. Untersuch.,’ neue Folge iv, 1892: 1. “ Das Sensible 
Nervensystem der Polychaten;” 2. ‘‘ Das Sensible Nervensystem der Mol- 
luscen.” Compare also Lenhossék, ‘Arch. mikr. Anat.,’ 39, 1892, and 
Retzius, ‘Biol. Untersuch.,’ neue Folge iii, 1892, for similar cells in Lum- 
bricus. 
