tially similar. The large tract of descending neurites shown in Fig. 37 passing from the facial lobe arises from the lateral part of the lobe, while the ascending secondary tract, or central gustotory path, takes its origin from the more mesial portion of the dorsal surface. These chief gustatory neurones of the facial lobe are like those of the vagal lobe in staining reaction, position and general relations. They are, however, smaller with more slender dendrites. One of them is shown in the dorsal

dorsal sec. neurone

Fig. 35. Portion of a transection though the cephalic end of the right facial lobe of Ameiurus nebulosus. GOLGI method. X 60.

The communis (gustatory) root of the facialis (com.r. VII.) enters from below. Dorsally is a single impregnated chief secondary neurone whose neurite enters the secondary gustatory tract (s.g.t.), and below it is an intrinsic neurone of type II (in.).

part of Fig. 35 and another as seen from above in horizontal section in Fig. 36. Ventro-mesially of the facial lobe, especially its caudal part, is a region of sparse cells which extends caudad to join the intermediate nucleus of the vagal lobe. It will be termed the intermediate nucleus of the facial lobe and is strictly comparable with the corresponding region of cyprinoids.

سالم

Fig. 36. A secondary neurone of the dorsal part of the facial lobe of Ameiurus as seen from above. GOLGI method.

X 500.

Drawn from a horizontal longitudinal section passing through the extreme dorsal part of the facial lobe. The neurite extends ventrally at right angles to the plane of the section (cf. Fig. 35) and hence of course does not appear in this preparation.

The greater part of the chief gustatory neurones of the vagal and facial lobes, as we have seen, send their neurites into the ascending secondary gustatory tract, or central gustatory path (secondary vagus bundle of MAYSER). This ascending tract terminates in the secondary gustatory nuclei under the cerebellum, partly on the same side and in smaller numbers on the opposite side. These nuclei lie in the isthmus close under the cerebellum at the point where the body of this organ is joined by the valvula cerebelli. The two nuclei are connected

by a broad dorsal commissure, above which is a commissure of the acustico-lateralis centers lying under the lateral extensions of the cerebellum. They are enveloped on all sides by tracts of fibers running vertically between the cerebellum and the regions in the brain stem below and cephalad of the nuclei, the cerebellar tracts forming a sort of capsule around the grey nuclei, these relations being the same as already described for cyprinoids. The relations of this nucleus and its tracts are shown in Fig. 37.

The intrinsic neurones of these nuclei are rarely well impregnated in my GOLGI preparations. The fibers of the central gustatory path end for the most part in free arborizations among these cells without crossing. But some of the tract fibers are clearly seen to cross to the opposite nucleus through the commissure of the secondary gustatory nuclei, as MAYSER has stated.

The tertiary tract arises from the chief cells in the cortical portions of the nucleus. These are frequently impregnated

Fig. 37. A parasagittal section taken through the brain of Ameiurus nebulosus so cut as to pass through about the middle of one vagal and one facial lobe and the lateral part of the cerebellum (cf. Figs. 5 and 20). Drawn from a single GOLGI preparation. X 45.

The section shows nearly the whole course of the central gustatory path (sec.gust.t.), composed of neurites of the chief secondary gustatory neurones of the vagal and facial lobes which terminate in the secondary gustatory nucleus (s.g.n.) under the cerebellum. The origin of the facial portion of the descending secondary gustatory tract (desc.sec. VII.) is seen in the facial lobe. In the facial lobe there is also seen a portion of the lateral part of the communis root of the facial nerve (com. VII) passing up to arborize within the lobe. The neurones of the vagal and facial lobes, which were richly impregnated in the preparation, are omitted from the drawing for the sake of simplicity. Along the cephalic border of the secondary gustatory nucleus is the beginning of the secondary gus. tatory commissure (s.g.c.). The origin of the tertiary gustatory tract from the secondary nucleus is not shown, but the terminations of these fibers (gust.3) are illustrated in the inferior lobe.

Bundles of fibers from the tuberculum acusticum are seen under the facial lobe, where they decussate, and their termini in the nucleus lateralis mesencephali (torus semicircularis or colliculus) are also shown (sec. VIII). Under the cerebellum are the cerebellar tracts which envelop the secondary gustatory nucleus (c). Granules of the cerebellum are marked gr.; those of the valvula, g. The bodies of the Purkinje cells of the cerebellum are indicated by dotted outlines. nuc.com., is the commissural nucleus of CAJAL.

and are of the same type as in cyprinoids. Their neurites, mingling with the tractus lobo-cerebellaris, pass down to end in the inferior lobe of the same side, essentially as already described for the carp. The ventral portion of this tract and its terminal arborizations are seen in Fig. 37.

The return path in the oblongata by way of the tractus lobo-bulbaris is also essentially as described for the carp.

SECTION V. SUMMARY AND GENERAL CONCLUSIONS.

In this section a brief summary of the facts as described in the preceding pages is followed by a discussion of some of the morphological considerations growing out of them.

The teleostean fishes generally possess taste buds freely scattered over the mucous surfaces of the mouth, gills and lips. The group of Ostariophysi is characterized by a very great development of this system of sense organs—in the siluroids in the outer skin and barblets and in the cyprinoids both in the outer skin and in still greater degree in the palatal organ within the mouth.

It has previously been shown experimentally that these fishes do in reality taste with their cutaneous taste buds, which are often called terminal buds and which have no relationship whatever with any variety of lateral line organs. Furthermore, while pure cutaneous gustatory stimuli can be localized by the fish, ordinarily both gustatory and tactile stimuli cooperate in the discrimination and localization of food objects.

The distribution and innervation of the organs of taste have been accurately determined for the siluroid fish, Ameiurus, all of them being innervated by the communis system of peripheral nerves. The nerves from the buds in the outer skin enter the brain exclusively by the facialis root; those from within the mouth by the facialis, glossopharyngeus and vagus roots, chiefly the latter. A special tuberosity of the brain, the lobus vagi, serves in fishes generally as the primary cerebral center for all gustatory nerves. This is greatly enlarged in some cyprinoids to provide for the taste buds in the palatal organ, and in both cyprinoids and siluroids there is another tuberosity de