PRENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. 191 



nerve is received by the otocyst nerve on its dorsal side (Plate 1, 

 Fig. 2, rm. L). This nerve is formed by an aggregation of fibres from 

 the tactile bristles of this segment of the anteunule, and runs almost 

 straight toward the median plane till it joins the nerve of the otocyst. 

 The fibres of the latter enter the anterior end of the brain ventral to 

 the optic neuropil, and median to the globulus ( Plates 1, 3, Figs. 

 4, 12) ; they extend backward to near the posterior end of the central 

 organ in an almost horizontal plane, lateral to the fibres of the antennular 

 nerve. They end in a region just anterior and median to the neuropils 

 of the secoud antenujB, branching into delicate dendritic fibrillae, which 

 form a well-marked neuropilar mass (Fig. 12, fbr'.). 



Fibres supplying the tactile hairs of the basal segment of the anteu- 

 nule eud in the same neuropil, while the main nerve to the antenuule 

 ends iu a closely oouuected fibrillar mass just median to it. Xo nerve 

 cells were found in the brain connected with the sensory fibres from the 

 otocyst. Association elements, with large dendritic branches, put these 

 neuropils into communication with the optic centres. One of these con- 

 necting fibres is shown in Figure 12 {fbr. ass.). Its cell, which sup- 

 posably exists, was not stained. According to Bethe's ('97, Taf. xxviii. 

 an.i ) experimental work on the brain of Carcinus maeuas some of the 

 otocyst fibres should end in the globuli. He could not demonstrate 

 such fibres, however, in his preparations of the crab's brain, nor was I 

 able to obtain conclusive evidence of such endings in the globuli of 

 Palfemonetes. 



d. Histology of the Nerve Elements. The nerve fibres of PalsE- 

 mouetes are relatively large ; those of the otocyst reach their greatest 

 size immediately before they enter the neuropil substance of the brain. 

 At that point in their course they are from 3 to 5 ya in diameter, not 

 including the nerve sheath. In a transverse section of the nerve the sep- 

 arate fibres show distinctly, as they are held apart by connective tissue. 



The ^An7/ar structure was made out definitely only in methylen-blue 

 preparations which had been well differentiated in process of fixation. 

 The gold-chloride method of Apathy, though tried several times, did 

 not give a successful reaction. Fibrillae were made out distinctly in 

 only one preparation, though some evidences of such structure appeared 

 m many. Figure 1.5 (Plate 4) shows a portion of a peripheral fibre iu 

 which many fibrils are seen running longitudinally. No single fibril 

 was traced any considerable distance, nor could any evidence of the 

 fibrils be found in the ganglion cells. The fibrill» are embedded in a 



