462 EDGAR J. ALLEN, 
the methylene blue has yielded by far the most satisfactory 
results, and the observations recorded in the present communi- 
cation have been made by its means. 
After experiments upon a number of embryos and larve of 
smaller Decapods (Palemon, Palemonetes, Crangon, 
Virbius), which failed largely on account of the rapidity with 
which the fine fibres assumed the beaded form, and subse- 
quently broke up under the influence of the reagent, an 
excellent object was found in embryos of the lobster (Homa- 
rus vulgaris) The fibres are here much coarser, and 
appear to be able to retain their normal shape for a longer 
time. Another great advantage of lobster embryos is their 
size and the comparative ease with which the thoracic ganglia 
can be exposed. All that is necessary for this purpose is, with 
a pair of needles, to burst the yolk and remove it, together 
with the investing membranes of the egg. It is well also to 
remove the connective-tissue bands (endosternite) which lie 
across the thoracic ganglia, especially over the portion imme- 
diately behind the esophagus. With a little practice this may 
be readily done in healthy embryos without injury to the 
underlying ganglia. These operations may be performed in 
sea water, or in dilute methylene blue solution. 
With regard to the strength of the methylene blue, it has 
been my practice to keep a standard solution of ,, per cent. 
in normal salt solution, and this has been diluted with fifteen 
or twenty volumes of a mixture of three parts of sea water to 
one of fresh immediately before use. The staining is most 
satisfactory when the temperature is from 20° to 25° C. 
The embryos, after being prepared as described, are placed 
on a slide, with the thoracic ganglia uppermost, and covered 
with methylene blue solution. The process of staining may 
then be watched under the microscope from its commencement. 
For this purpose no cover-glass should be used, and the object 
should be illuminated with an Abbé condenser, the diaphragm 
of which is left open. 
The stain enters the ganglia in two ways: (1) through the 
lateral nerves, and (2) through any wounds which may exist in 
