624 MR. E. B. POULTON ON THE [DcC. 18, 



Plate LV.). It now takes the form of a series of slit-like depressions 

 in the smooth epithelium beneath the papillate surface. There are 

 no mound-like elevations, and the whole appearance more resembles 

 that of the well-marked organ of certain higher mammals. Corre- 

 sponding with this, the sides of the depressions are crowded with 

 closely packed taste-bulbs, and the gland-ducts seem to begin where 

 the taste-bulbs end. Witliout the knowledge derived fi-om the pre- 

 ceeding species, there would be no suggestion that the gustatory part 

 of the depression is itself a gland-duct (see fig. xsxii. Plate LV.). This 

 well-marked organ is still behind the most complex organ of Eodents 

 in that there is no indication of a lateral area upon which the depres- 

 sions are arranged, and no elevation of the ridges between the depres- 

 sions ; in fact the attention is merely directed to the slits, while in the 

 more complex organ the ridges also attract notice. Further the slits 

 are less uniform in size and less regular in arrangement than in the 

 well-marked organs of Eodents, &c. The filiform papillffi {I. f. p.) 

 have the usual arrangement ; many of them have the shape of a 

 triangular flap attached along the base. The circumvallate papilla 

 (c. V. p.) are arranged in the normal manner ; the two anterior 

 papillae are smaller than the posterior and of a different shape (com- 

 pare figs. XVI. and xx.), the former following the type of Halmafurus 

 and Macrojms, the latter resembling the papillae of higher mammals. 

 The upper surface of the organ is, as usual, covered with coronate 

 pajnllse. This is also true of the other tongues figured (and probably 

 of all Marsupials). 

 Fig. IX. Natural size. The same tongue (of Phalangista vidpina), seen from the 



right side. The references are the same as those previously used. 

 Fig. X. Natural size. The tongue of Belidcus brevkcps, seen from above. There 

 is a lateral organ present (hai-dly visible from above) in the same 

 situation as that of Phalani/isfa and of similar structure. The relation 

 of the anterior circumvallate papillae (c. v. p.) to the posterior papilla 

 is also similar to that described in FhalangMa (compare figs. xv. and 

 XVII.). The anterior contour of the tongue may not be correct. 

 The drawing was made from a spirit specimen in which the tongue 

 was bitten tlirough at the tip. and the anterior narrower part was bent 

 down abruptly. In the figure I have assumed that this was accidental, 

 and this was probably the case. 

 Fig. XI. Natural size. The tongue of Didelphi/s qidca seen from above. The 

 cavity around the epiglottis {Ep.) has been widened by separating 

 the walls with a needle (drawn in the figure). The normally arranged 

 circumvallate papillfe {c. v. p.) appear to resemble one another, and 

 to follow the higher type. It was impossible to be certain of this, 

 because there had been considerable alteration in the spirit specimen. 

 There appears to be no lateral organ. The transverse ridges in front 

 of the circumvallate papillw may be accidental. The antei-ior contour 

 of the tongue may not be quite correct. The coronate papillae covering 

 a well-marked patch beliind the tip (s. c. p.) are peculiarly modified, 

 a change being very distinct to the naked eye. The posterior part of 

 the ring of secondai-y papillae is occu)5ied by a single, very strong, 

 cornified, recurved hook (see fig. xxii. Plate LV.). 

 The seven succeeding figures (xii. to xviii.) illustrate a gradual transition 

 from the circumvallate papillae of Ornithorhynchus to those met with 

 in the higher mammals. This transition is from a bilaterally symme- 

 trical structure, with taste-bulbs developed over its entire surface, to 

 a radially symmetrical structure with the taste-bulbs confined to a 

 belt round the base of the papilla. At first the papilla is but slightly 

 withdrawn from the surface (fig. xii.) ; then it is deeply placed at the 

 bottom of a narrow cleft (fig. xiii.) ; it then gi-adually emerges through 

 a long series into the usual type of higher mammals (figs. xiv. to xviii.). 

 Fig.xu.X 14'.5. Transverse section of the posterior bulb-bearing i-idge of 

 Ornithorhynchus. It is probable that tiiste-bulbs were first developed 



