ly»3.] TONGUES OF THE MARSUPIALS. COl 



posteriorly also). The resemblance between the larger and smaller 

 mounds is very complete, and the latter are true gland-ducts and 

 apparently nothing more. Above the lateral organ the densely papil- 

 late surface is limited by an irregular row of filiform papillae extending 

 posteriorly and superiorly beyond the lateral organ. These papillae 

 are probably tactile, and their position is constant in Marsupials (as 

 far as I have observed), even in the absence of a lateral organ. The 

 two anterior circumvallate papillae are situated (11 mm. apart) at 

 the level of the posterior end of the lateral organ. The posterior 

 papilla is set very far forward in this species, so that the three are 

 nearly in one straight line, the posterior angle being very obtuse. 

 All that can be seen of the papillse from the surface is a funnel-shaped 

 depression (about 1 mm. across at the widest part), at the bottom of 

 which the apex of the papilla can generally be detected, directed 

 forwards (see fig. iv. Plate LI V. taken from the larger tongue). The 

 opening leading into the involution containing the central papilla was 

 entirely invisible from the surface, and the papilla was only dis- 

 covered accidentally. The opening may be surrounded by a sphincter 

 of smooth muscle ; and it is probable that the central opening is not 

 really smaller than the others, since the papillae and the involutions 

 are quite similar. A further proof of its contracted state was found 

 in the folded condition of the inner surface. The coronate papillae 

 crowd closely upon the openings in the smaller tongue, but in the 

 larger separate opening (fig. iv. Plate LIV.) they become less con- 

 spicuous posteriorly. Immediately round the openings there is an 

 irregular ring of short simple papillae (fig. xix. Plate LIV., which 

 also indicates the very constricted passage leading into the involution 

 for the posterior papilla of the smaller tongue). 



Minute Structure. — L Gustatory Structures. 



A. The Circumvallate Papillce.— -The remarkable shape and ex- 

 treme protection of the papillae is shown in fig. xiv. Plate LIV. The 

 taste-bulbs are seen to be very numerous ; there are over 30 tiers, 

 and those round the central thickest part contain 80-90 in a single 

 tier (see fig. xxi. Plate LV.). They are closely packed round the 

 circumference, but there are generally one or two places in each 

 section where they are absent, and they cover the whole surface of 

 the papilla except a small part below the apex, which is the only 

 unprotected region (see fig. xiv. Plate LIV.). There is I believe no 

 doubt that the mouth of the depression can be closed upon the apex 

 of the papilla, and that thus the delicate end-organs are completely 

 protected. The mechanism for opening and closing is, however, 

 very uncertain : smooth muscle-cells may be present in the mucosa 

 parallel with and just outside the involution; such fibres would act 

 as a dilating agency, aided by the contraction of other bands, which 

 may also contain smooth muscle, and which radiate horizontally 

 outwards from the thickened mucosa round the mouth. The 

 closure of the mouth may be effected by a sphincter of smooth muscle- 

 fibres, but in all these cases I cannot be certain as to the existence 

 of the smooth muscle. By a different mechanism the papilla can 



