In this and other arthropods which I have studied, it seems to me to be quite characteristic of the nervous system that many parts show fine fibrillæ more clearly than they are seen in vertebrates. This may in part be due to the nature of the insulating and supportive apparatus. As in _Carcinus_, described by Bethe, the optic tract enters the mesal side of the globulus and splits up into smaller and smaller parts, and is at last lost in the minute network of fibrils and supporting substance. Large bundles from the outside may be seen as dark masses here and there. These last are held in place in the section by many connecting strands which join the fibers from all sides. Some may be conducting fibrils, but it is hard to distinguish these from supportive. Probably most of the conducting fibrils leave at or near the termination of the thicker part of the fiber. The denser parts of the nervous system of this and other arthropods, such, for instance, as the material of the globulus, are composed for the most part of ultimate fibrillæ whose relationships at these points can only be conjectured at present because of their minuteness, their great abundance, and because of the intermingling of supportive or other materials of several little understood sorts. An extensive comparative study of these denser masses with various reagents should yield some interesting results. Tigroid substance, mostly in the form of dots and flakes, was recognized, but not studied by special stains. The cells are surrounded by a dense capsule of connective substance, and in some cases the peripheral zone of the cell next the capsule is light. In some, this light zone is speckled with dark dots or lines. Some of these may be the ends of fibrillæ--in fact, some fibrils were traced--others may be tigroid substance, or possibly the bodies recognized by Poluszynski in some Crustacea, although his are stained by other methods. PAPERS MENTIONED _Bethe, A._ 1898 Das Nervensystem von Carcinus maenas. Arch. f. Mic. Anat. Bd. 51. _Poluszynski, G._ 1911 Untersuchungen über den Golgi-Kopsch'schen apparat und einige andere Strukturen in dem Ganglionzellen der Crustaceen. Bull. Acad. Sc. Cracovie. Figure 1. Outline of the cephalothorax of _Loxorhynchus_, showing the position and size of the nervous system. One-half natural size. Figure 2. Brain of _Loxorhynchus_ from above. ×10. o, Ocular nerve; m, oculomotor; t, tegmental nerve; a, first antennal nerve; b, second antennal; c, connective. Figure 3. Nerve cell with fibrils from the brain. ×900. Figures 4 and 5. Nerve cells near each other in the brain fibrils are shown. ×900. Figure 6. Neuroblast from a doso-median mass of the brain. ×900. Figure 7. Neuroglia cell with branches from the brain. ×900. Figure 8. Two fibres breaking into fibrils. From the brain. ×900.