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Show 622 MR. E. B. POULTON ON THE [Dec. 18, organ, and hence the series (figs, xiv-XVIII. Plate LIV.) in which the most protected forms show independent evidence of their primitive condition. With the most perfect protection, there is also the presence of bulbs over the whole of the papillary surface ; and as the papilla becomes less protected, the bulbs gradually sink into their normal position of a zone round the papillary base. Even in the highest marsupial papilla? there is some trace of the original protection in the presence of a much constricted base. In some marsupial tongues both conditions coexist, and the less protected, radially symmetrical form is the posterior (i. e. the papilla most sheltered by its position, and thus able most quickly to abandon the old excessive protection). It has been much in favour of this theory that I have been able-in more than one part of the subject-to confirm previous suggestions by subsequent work. As to the primitive triangle of circumvallate papillae, I have no doubt that we have here the ancestral form of the inverted V arrangement in many higher animals (e. g. man). It is possible that, the above being the history of the primitive circumvallate papilla?, in some cases their number may be added to by direct development from fungiform papilla?; but this is only a suggestion founded on a superficial examination. EXPLANATION OF PLATES LIV. & LV. Fig. i. Natural size. The back part of the tongue of Halmaturus ualabatus seen from the right side. The upper surface is seen to be densely papillate, the papillae being of the coronate type (i. e. papilla? surmounted by a circle of fine, hair-like, generally recurved, secondary papillae, the whole of mechanical function, and as far as is yet known peculiar to and always present in Marsupials; see fig. x x v m , Plate LV.). f. p. Fungiform papillae of the normal structure; few in number and scattered irregularly among the coronate papilla, above the lateral line of junction with the non-papillate surface. I. f. p. Lateral filiform papilla?, forming the limits of the papillate surface at the posterior part of the junction with the non-papillate surface. These large and probably tactile papillae are very constant in this position in the tongues of Marsupials and probably of other Mammalia. The lateral gustatory organ, when present, is to be found (as in this tongue) in the non-papillate surface just below the anterior part of the row of filiform papillae, l.g.o. Lateral gustatory organ, here presenting the appearance of a row of circular elevations with a crater-like depression (generally somewhat elongated) on the summit of each ; beneath these elevations is a longer, less regular row of smaller but otherwise apparently similar elevations, gld. d ; the depressions on the summits of these latter are gland-ducts leading from glands of mucous type. No taste-bulbs are to be found in the walls of the ducts, but they are present in small numbers in those of the larger elevations (/. g. o.). But in other respects these last depressions are precisely similar to the former; they lead into glands of serous type, and all their relations are those of gland-ducts (see fig. xxxi. Plate LV.). We therefore have here the simplest form of lateral organ-a row of simple gland-ducts, in the walls of which scattered bulbs are developed. From this type w e can pass by gradual stages to the complex lateral organ of Bodents, in which there is but little indication of the true origin, except when looked at in the light derived from the study of such a tongue as that of Halmaturus. The arrow ( $*-) in all cases points |
