STUDIES ON THE NERVOUS SYSTEM OF CRUSTACEA. 485 
upon judging properly the moment to stop the staining process. 
If the latter be allowed to continue for too long a time, the 
nervous elements lose their colour, and a diffuse staining of 
other tissues takes place. 
It is necessary to make a large number of preparations to 
obtain satisfactory results, and care must be taken not to pull 
the tissue about very much in getting it ready. It must also 
be so arranged that all the nerves lie freely exposed to the 
methylene blue solution, and not covered by other tissues. If 
these precautions are attended to, very beautiful results can be 
obtained. 
The diagram, fig. 1, represents much the appearance of a good 
methylene blue preparation, and the individual elements there 
recorded are taken from actual preparations. The figure repre- 
sents the nerve-ring turned through nearly a right angle until it 
comes to lie upon the anterior surface of the cesophagus, as it 
will do in preparations made as described above. From the 
brain (Br.) the two cesophageal commissures run down upon 
either side, and contain numerous stained fibres which often 
are beaded in various ways. This beading, which will be after- 
wards discussed in more detail, is not the natural condition of 
the fibre, and can give rise to a variety of appearances, some 
of the more typical being recorded in the commissures drawn 
in the figure. 
About one third of the way down the commissure is the 
ganglionic swelling (com. gang.) from which the nerves of the 
stomatogastric system spring. Behind this swelling lies the 
transverse bridge (¢7. dr.), which runs from one commissure to 
the other, and in the natural position of the parts is situated 
immediately behind the esophagus. It is worth noting that 
all the fibres observed to pass through this transverse cord 
come down the commissures, a few possibly from the com- 
missural ganglia, the majority from the brain. 
From each of the commissural ganglia two nerves spring, 
which unite with their fellows of the opposite side in what is 
practically a somewhat diffuse ganglion, which lies in the 
middle of the anterior surface of the esophagus, and will be 
