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STUDIES ON THE NERVOUS SYSTEM OF ORUSTACEA. 463 
the ganglia themselves. By taking advantage of the latter 
fact, many of the results to be recorded have been obtained. 
The ganglionic cord has been injured or cut across in various 
places, and some elements can be got to stain with considerable 
certainty by wounding in particular places. No very definite 
directions, however, can be formulated on this point, but a 
little practice will give the desired result. Accidental surface 
wounds, made when preparing the embryo, are often of great 
value in this way. 
The preparations may be fixed in a solution of ammonium 
picrate containing an excess of ammonium carbonate, and 
mounted in glycerine diluted with an equal volume of the fix- 
ing solution. A large number of preparations were fixed in 
this way. They do not appear to be quite permanent, but 
preparations which I have kept for five months, although they 
have lost some of their original brilliancy, are still of great 
value. On the whole, however, it was found more practical 
not to fix at all, but to examine a very large number of prepara- 
tions in the fresh state. A number of diagrams of the ganglia 
similar to the ground plan of fig. 1) were traced, and into one 
of these the results of a preparation were drawn. In this way 
from fifteen to twenty preparations could be made, and their 
results recorded, in a day. Not only is the number of pre- 
parations made greater, but the results obtained are more 
numerous than if the preparations were fixed, for in order to 
obtain good permanent preparations it is essential to stop the 
staining process when it is at its best. If, however, the embryo 
be allowed to remain in the blue solution, although the colour 
in most of the elements fades, individual fibres, and especially 
fresh cells, may continue to stain, and the results thus obtained 
are often the most valuable. 
In dealing with the results obtained by methylene-blue 
staining, it must be always borne in mind that one can never 
be quite sure that the whole of the element has taken up the 
blue. With this reservation, the results to be recorded, which 
have been obtained after examining many hundreds of pre- 
parations, are those only which I regard as practically certain, 
