OCR Text |
Show 606 MR. E. B. POULTON ON THE [Dec. 18, The ring of secondary papilla? is less regular in Halmaturus than in Perameles &c, and it is common to find single papilla? within the ring (i.h.p., fig. XXVIII. Plate LV.). Between the coronate papillae isolated hair-like papilla? are common, rising singly from the epithelium. In all respects these resemble the hair-like papilla? of the coronate rings. (They are shown in fig. XXVIII. Plate LV., s.h.p., and in vertical section in fig. X X V I I . Plate LV., s.h.p.) These isolated slender papilla? with no tendency to coaksce into rings are very characteristic in tongues which in other respects also show traces of more primitive affinities than those of other Marsupials. (The posterior part of the tongue of Ornithorhynchus is covered with closely set single hair-like papilla?, very much resembling the papillae here described, and agreeing in the important point that each hair-like papilla possesses but a simple papillary upgrowth.) The coronate papilla? are of large size, and there are only about 10 to the square millimetre close to the posterior circumvallate papilla. A little anteriorly (by the anterior circumvallate papilla?) they become rather smaller, and I counted 12 to the square millimetre. In ascending from the smooth to the papillate surface, the long papillary processes of the former first bear simple papillae ; these form an irregular row (one or two deep, and sometimes absent) and then coalesce into the coronate papilla?. There are a few of these simple papillse, bent upwards so as to be almost parallel with the surface of tbe tongue, below the lateral organ in some sections. The coronate secondary papilla? curve upwards from the sides towards the middle of the tongue (see fig. xxix. Plate LV.) ; but this is not so marked as in Phalangista, at any rate in the posterior part of the tongue. The secondary papillae of the upper surface are curved backwards; but this is very slightly marked posteriorly, where the coronate papilla? are tall and slender ; while anteriorly (in the piece of tongue in m y possession) they become shorter, stouter, and the hair-like secondary papillae much recurved (see fig. XXVII. Plate L V.). The epithelium is immensely thickened in passing from the smooth into the papillate region (see fig. xxxi. Plate LV., s.e., where the transition is taking place, and compare the thickness with the less magnified fig. XXVII. Plate LV., which is taken in the middle line of the papillate surface). Although the epithelium changes in thickness, the four layers of the complex epithelium can be detected in it and euter into the coronate papilla?. This is best shown near the transition. (See fig. xxix. Plate LV., which represents dia-grammatically the arrangement of the four layers in a single coronate papilla close to and above the lateral organ. The section is of course vertical and transverse, and the curve of the secondary papillary processes is upwards. The layers correspond to those in fig. xxxi. Plate LV. In other parts of the papillate surface the distribution of the corneous layer (2) would be more symmetrical upon the secondary papilla?.) W e thus have a proof that the layer (2) previously described is truly corneous, inasmuch as in these fine processes, of mechanical use, it rises to the surface and is confined to the effective side, or both sides where both are effective. The very |