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



Minute Structure. — I. Gustatory Structures. 



A. The Gircumvallate Papilla. — All three are probably similar in 

 structure, and seem to be intermediate between the Halmaturus type 

 (fig. XIV. Plate LIV.) and the higher form approaching radial sym- 

 metry. The symmetry here is, I believe, decidedly bilateral, the 

 papillae distinctly directed forwards, and the protection extreme ; but 

 in none of these points do the papillae equal those of Halmaturus. 

 There were some indications that the posterior papilla is less 

 inclined than the anterior, but I am not certain that the appearance 

 is genuine. The posterior involution is also surrounded by a 

 prominent rim with papillae upon it. Nothing could be ascertained 

 as to nerve-cells in the papillae. I could not decide as to the height 

 to which the bulbs extend on the papillae — probably up to the point 

 at which the sides begin to slope sharply inwards to form the 

 summit, which seems to end in a simply pointed apex. The base 

 of the papillae seems to be invaded by glandular tissue. 



B. The Lateral Gustatory Organs. — These are much the same as 

 in Halmaturus, but are more advanced ; they do not obviously 

 represent gland-ducts, but suggest depressions into which the latter 

 enter. The mounds on which the farrows open are more prominent 

 than in Halmaturus. 



C. The Fungiform PapillcB. — These papillae contain bvdbs and are 

 richly supplied with nerves. The epithelium below the tip is 

 smooth, but probably tactile from the abundance of nerves beneath 

 it. 1 could not distinguish any difference between the large and 

 small papillae of the tip, or between the papillae of the tip and 

 those situated posteriorly. I should like to work at this point 

 again w'ith specially prepared material. 



II. Mechanical and Tactile Structures. 



A. The Coronate Papilla. — On the upper surface of the tip hori- 

 zontal sections prove that there are generally 9-12 secondary papillae 

 forming an anterior horseshoe, and a single large posterior papilla, 

 indicating the beginning of that peculiar modification of the coronate 

 type which reaches its culmination in Didelphys. This posterior 

 papilla is especially coruified, and its base tends to pass forward as 

 two horns ; it is broad at the base, pointed above, and it must be 

 concave from side to side anteriorly. Its papillary ujjgrowth is very 

 large and triangular, the angles tending to pass anteriorly with the 

 horns. The coronate papillae of this part of the tongue very much 

 resemble the transitional forms tliat pass into the strongly marked 

 region of Didelphys. The coronate papillae are oval antero-pos- 

 teriorly. In the anterior horseshoe there are occasional irregu- 

 larities, but isolated hair-like papillae are absent in this part of the 

 organ. Vertical longitudinal sections confirm the conclusion derived 

 from a study of horizontal sections. There are about eleven 

 papillae to the square millimetre. 



Midway between the tip of the tongue and the anterior circum- 

 vallate papillae, the isolated hair-like papillae are very abundant. 



