«0 TUCKERMAN. [Vol. VII. 



is marked by a longitudinal median ridge leading from the 

 frsenum to the tip, and the papillate surface is impressed anteri- 

 orly by a mesial groove. The fungiform papillae are largest 

 and most abundant at the sides of the organ, a little above 

 the junction of the papillate and non-papillate surfaces. The 

 greater part of the dorsum is beset (as usual in the Marsu- 

 pialia) with closely packed papillae of the compound filiform 

 type. The circumvallate papillae are three in number, and 

 form an isosceles triangle. The posterior papilla is small, but 

 clearly defined, and is distant about 15 mm. from the base 

 of the tongue. The anterior papillae are 8 mm. apart, and 

 are very deeply set. Their apices barely reach the level of 

 the lingual surface, and can be seen only by pressing apart the 

 edges of the trenches. The region posterior to the triangle 

 formed by the circumvallate papillae is marked by a number of 

 subparallel rugae, which traverse the entire width of the dorsum. 

 The lateral organs of taste are below the line formed by the 

 junction of the two surfaces. They present a single row of mi- 

 nute openings. A short distance below the lateral organs is a 

 longer but somewhat less regular row of openings. These are 

 smaller than those of the lateral organ, and are spheroidal in 

 shape. They are obviously the mouths of mucous ducts, the 

 latter being very abundant in this region. Above the lateral 

 organ, but at some distance from it, is the usual limiting fringe 

 of filiform papillae. 



The Filiform PapillcB. — These papillae follow the usual 

 marsupial type (first described in detail by Poulton), and resemble 

 quite closely those of Phalangista. They measure 0.3 mm. in 

 diameter at the base, and are only 0.02 mm. apart. At the 

 anterior limits of the middle third of the dorsum there are about 

 fifteen papillae to the square millimetre of surface. Each papilla 

 breaks up into a number of secondary hair-like processes (usually 

 nine), forming an incomplete ring round the outer portion of the 

 main papillary trunk. Posteriorly the circle is not infrequently 

 closed by a single process of much stouter growth and which 

 is cornified at the tip. 



GUSTATORY STRUCTURES. 



The Circumvallate PapillcB. — These papillae exhibit the 

 characters pecuHar to the Marsupialia. They are more prim- 



