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Show 604 MR. E. B. POULTON ON THE [Dec 18> (even under this power) basement membrane. The fibrils often expand at their termination, becoming funnel-shaped. Such appearances are observed over the whole proximal surface of the bulb and not merely at its centre. It was really impossible to be certain in the identification of these fibrils as nervous, and yet there are some fibrils which can be considered nervous with a very high degree of probability. These are distinct under comparatively low powers as sharply defined dark fibrils that pass straight through this layer from the fibrous layer towards the taste-bulbs. These fibrils confer a radiate appearance upon the subepithelial layer (see fig. xxi. Plate LV.). Round or oval, deeply-staining nuclei are very characteristic of this layer, and are obviously related to the nervous elements, as they are almost completely limited to the region of the end-organs. These nuclei belong to small multipolar cells continuous with some strands of the network ; but it seems more probable that they belong to a special supporting connective tissue (such as the neuroglia) than that they are nervous. This subepithelial layer bears a strong resemblance to certain retinal layers, and is probably identical in structure (both consisting essentially of the unravelled elements of supporting and nervous tissues arranged in fine interpenetrating networks, as has been mentioned). These layers and their relation are better seen in longitudinal than in transverse sections of the papilla (see fig. xx. Plate LIV., which shows the same arrangement in Phalangista). B. The Lateral Gustatory Organs.-When a section is taken at right angles to the long axis of one of the depressions (upon one of the elevations previously described), the latter is seen to be the mouth of a narrow chink which is obviously the duct of a gland (see fig. xxxi. Plate LV.), in the epithelial walls of which a few taste-bulbs have been developed. The lateral ducts sometimes open into the chink above the taste-bulbs, and below the points where the latter occur the main duct breaks up into smaller tubes. Horizontal sections show that the narrow ducts into which the depressions open are always slit-like, although the latter may appear to be circular, and the long axis of the slit is always at right angles to the inferior limit of the papillate surface above. In this respect the primitive lateral structures of Halmaturus are similar to the furrows of the lateral organ in higher animals. Although the bulbs are scattered irregularly in vertical sections, their arrangement is much more even in sections taken horizontally. It is therefore probable that the real arrangement is in regular tiers, but that the tiers themselves do not follow one another regularly. The subepithelial layer is not strongly developed beneath these bulbs, but traces of it can be distinguished. The nerves approach the bulbs from the sides, running horizontally beneath the epithelium for a considerable distance. Ganglion-cells are very numerous in little groups on the nerves. The cells are enclosed in distinct nucleated capsules. The glands into which the ducts of the lateral organs lead are of course serous. The smaller gland-ducts which open below and in front of the lateral organs (see fig. i. & c Plate LIV.) lead down deeply into |
