No. 2.] OlV THE Gl/SJAJVA']' ORGANS. 155 



stains quite deeply in lucmatoxylin. The secondary papillae of 

 the middle dorsal region, in which the cornification of the epi- 

 thelium is further advanced, are much less affected by staining 

 reagents. Externally the papilla; are covered by a thin layer 

 of ordinary stratified epithelium. 



This type of compound filiform papilla; is characteristic of 

 the marsupial tongue, if not peculiar to it. The papillae, as 

 suggested by Poulton, who first described them,i have doubtless 

 been modified in a special manner for the capture of small 

 insects. The same observer has suggested the term "coro- 

 nate" for those papillae which are surmounted by a ring of 

 recurved hair-like processes, and the term "fasciculate" for 

 those in which the appearance is more brush-like. For the 

 compound filiform papillae of Didclphys virginiana the latter 

 term would be more closely descriptive than the former. 



Gustatory Structures. 



The Circtimvallate Papillce. — The posterior papilla follows 

 quite closely the type common to the higher animals. The 

 anterior pair resemble the corresponding papillae of Belideus 

 and Phalangista, but are further advanced. The posterior 

 papilla measures 0.75 mm. at its widest part, and is 0.70 mm. 

 in height. The upper surface is somewhat uneven, and over- 

 tops slightly the adjacent lingual area. The trench encircling 

 the papilla is narrow and fairly uniform in breadth. The an- 

 terior papillae are somewhat elongated, and average 0.60 mm. in 

 breadth and 0.90 mm. in height. They are deeply set, their 

 summits barely reaching the level of the general lingual surface. 

 Serous glands are abundant beneath and at the sides of the 

 papillse, and their ducts open into the trenches at their base 

 and lower part. 



The taste-bulbs of the posterior papilla are mainly confined 

 to the inferior half of the lateral area. They are disposed in a 

 zone of twelve to fourteen closely packed tiers. The bulbs of 

 the anterior papillae are similarly arranged, though with an 

 increased number of tiers. There are about sixty-five bulbs in 

 a tier. The bulbs of both regions are fairly uniform in size and 

 shape, and measure 0.054 mm. in length and 0.034 mm. in 

 l^readth. 



1 "On the Tongues of the Marsupialia," Proc. Zool. Soc, 1883. 



