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 I'apid 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. PALiEiMOXETES VULGARIS StIMPSON. 



1. Strvcture of the Otocyst. 



a. Sac. This is situated, as in all decapods except the Mysidse, 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). Tlie 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 

 anteimular nerve, the cut end of which is shown at n. at. 1 (Plate 1, 

 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' ]nl. 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- 



