180 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
readily, and on the rapidity of its penetration depends, in a large meas- 
ure, the success of fixation. Gold-chloride and Golgi preparations were 
useful only for supplementing and controlling the results obtained by 
methylen blue. Both the rapid and slow processes for silver impregna- 
tions gave fairly good preparations, but by no means as complete or 
constant results as methylen blue. Ranvier’s gold-chloride method, 
in which formic acid is used for reduction, was very uncertain in its 
action on nervous tissue, but was quite useful in bringing out fine cell 
processes in the sensory hairs. 
3. Structure and Development. 
I. PALZMONETES VULGARIS STIMPSON. 
1. Structure of the Otocyst. 
a. Sac. This is situated, as in all decapods except the Myside, in 
the basal segment of the antennule, nearly filling its cavity. Its out- 
line as seen from above (Plate 1, Fig. 1) is nearly ovate, being well 
rounded posteriorly, though suddenly becoming pointed at its anterior 
end. In individuals of medium size (30 mm. long) its average dimen- 
sions are 0.66 mm. in length, 0.63 mm. in width, and 0.33 mm. in depth. 
In longitudinal section (Plate 1, Fig. 4) its outline is somewhat kidney- 
shaped, its length being about twice its depth, and its ventral wall 
projecting into the lumen. ‘Transverse sections through the basal 
portion of the antennule (Figs. 2, 3) show that the lumen of the otocyst 
is from one half to two thirds as wide as the antennule at this point. 
The chitinous wall of the sac, which is extremely thin, is continuous 
with that of the antennule (Fig. 3). The hypodermal cells form a 
single layer, except in the sensory region of the sac, where they are 
elongate and several layers thick. Median to the otocyst passes the 
antennular nerve, the cut end of which is shown at x. at. 1 (Plate1, 
Fig. 2), and directly below it lies the large muscle of the segment. 
Otoliths occupy the median and posterior portion of the lumen, and 
nearly conceal from view the sensory hairs (Fig. 3, set. ot.). In para- 
sagittal sections (Fig. 4) is to be noticed the close proximity of the 
brain (n’ pil. opt.), which is not more than 0.22 mm. posterior to the 
sac, and projects somewhat into the base of the antennule ; the sensory 
cushion, or prominence (crs. sns.), bearing the stumps of a few severed 
hairs, is also to be seen. 
The long axis of the otocyst is not coincident with that of the anten- 
