STUDIES ON THE NERVOUS SYSTEM OF CRUSTACEA, 43 
II. ABDOMINAL GANGLIA. 
Mertuop or Preparation.—Staining of elements in the 
abdominal ganglia can be observed in two ways. In the case 
of embryos at an early or medium stage of development which 
have been prepared, as described in Part I, for the staining of 
elements in the thorax and in which the abdomen is allowed 
to remain undisturbed, fibres which have taken up the methylene 
blue in the thorax often continue to absorb the colouring 
matter in the abdomen, and the cells with which they are con- 
nected are thus brought to light. The best results for the 
abdominal ganglia can, however, be obtained by special pre- 
paration of embryos which are very near the hatching point. 
In such embryos the abdominal ganglia may be dissected out 
from the surrounding tissue by careful manipulation with 
needles. Special care must be taken not to injure or stretch 
the ganglia and their continuity with the ganglia of the thorax 
should be maintained. Ifthe embryos, thus prepared, be placed 
with the dorsal surface uppermost in very dilute methylene 
blue (1: 100,000 may be used to commence with, and the 
strength gradually increased), satisfactory staining of many of 
the elements of the abdomen will soon take place. 
A variation of this method, which often gives good results, 
consists in removing, or even simply tearing, with needles the 
cuticle on the ventral surface of the abdomen (after having 
first turned the abdomen backwards, and caused it to lie in a 
line with the thorax), and allowing the embryo to lie in the 
methylene blue with the ventral surface uppermost. In this 
case, as soon as the staining is thought to be satisfactory, the 
ganglia must be dissected out before they are examined. A 
cover-glass may be placed upon them, and the elements rapidly 
drawn, or the preparation may be fixed with ammonium picrate, 
and mounted in glycerine diluted with an equal volume of 
saturated solution of the picrate. Such preparations, however, 
only retain their full colour for a comparatively short time. 
For practical purposes a large number of fresh preparations, 
examined with a cover-glass, have been found more instructive 
