152 TUCKERMAN. [Vol. IV. 



The researches which are recorded in the following pages 

 were carried on in the Biological Laboratory of Clark Univer- 

 sity, Worcester, during the winter of 1889-90. 



I am greatly indebted to the University for kindly obtaining 

 much of the material upon which this paper is based. I also 

 desire to express my thanks to Mr. Agassiz, Curator of the 

 Museum of Comparative Zoology at Cambridge, Dr. Whitman, 

 Professor of Animal Morphology in Clark University, Mr. 

 Bumpus, Associate Professor of Biology in Brown University, 

 and Dr. J. N. Hall, of Sterling, Colorado, for their kindness in 

 supplying me from time to time with valuable specimens. The 

 greater part of the material had been kept in dilute or ordinary 

 spirit. Of the remaining specimens, some were hardened in 

 absolute alcohol, others in osmic acid, and still others in 

 Miiller's fluid, either alone or in a mixture of Miiller's fluid and 

 alcohol in various proportions. The parts of the specimens 

 intended for microscopical examination were embedded in 

 celloidin, and for staining the tissues the usual reagents were 

 employed. 



A table contaming some comparative data respecting the 

 gustatory structures of the forms considered in the following 

 pages is appended to the paper. 



The Tongue of Didclphys virgiuiana. 



I examined several tongues of DidelpJiys, most of them from 

 adult animals. All of the specimens had been hardened in 

 spirit before I received them. 



General Description. — The organ measures 75 mm. in length, 

 18.5 mm. in breadth, and 13 mm. in thickness. Anteriorly it is 

 free from the frasnum linguae for 34 mm. The under surface is 

 smooth and marked by a longitudinal median ridge extending 

 from the fraenum to the tip. On either side of the ridge is a 

 wide but shallow groove. The tip, which is somewhat obtuse, 

 is bordered by a delicate fringe of simple filiform papillae, the 

 latter being probably tactile in function. The upper surface is 

 impressed by a number of transverse furrows, corresponding to 

 the roof of the palate. Anteriorly it is covered with closely 

 packed compound filiform papillae, to be presently described. 

 The fungiform papillae are of fair size, and appear to be normal 

 in structure. They are not, however, very numerous, and, as 



