16 THE GUSTATORY ORGANS, BY TH. W. ENGELMANN. 



ring dichotomous divisions. Our description has been taken from 

 fresh specimens placed in serum and diluted glycerine. 



The gustatory disks are elliptical or circular sharply defined 

 epitjielial plates, with a transverse diameter of about O15 to 

 O35 of a millimeter, and a thickness of 0'04 to 0'05 of a milli- 

 meter. Their inferior surface adheres firmly to the nerve 

 cushion, whilst the upper forms the whole terminal surface 

 of the papilla. The " nerve-epithelium," which composes the 

 whole mass of the gustatory disk, is distinguished from the 

 ordinary columnar and ciliated epithelium by the circumstance 

 that it is optically perfectly homogeneous and very transpa- 

 rent, and is also very clear by transmitted light. When seen 

 in thick layers, it presents a faint tinge of yellow. 



It adheres more firmly to the papilla than the remaining epithelium. 

 The cells also of which the disk is composed cleave to one another 

 much more intimately and strongly than ordinary epithelium. 



Leydig first called attention to the fact that the epithelium covering 

 the free surface of the papillas fungifornies differs from other epithelia. 

 Later observers, with the exception of Fixsen, have uniformly cor- 

 roborated this statement. Billroth, and especially Ernst Axel Key, 

 have given full and minute descriptions of the nerve epithelium. 



The gustatory disks of the Frog are composed of several 

 kinds of cells, of which in all probability only one kind, the 

 forked cells, are continuous with nerve fibres. Two other 

 kinds, the broad goblet-cells and the slender columnar cells, 

 appear to be more of an indifferent nature, like the investing 

 cells of the gustatory cups. These three kinds of cells are so 

 arranged in the gustatory disks, that the bodies of the goblet- 

 cells form a single layer on the upper surface of the disk, whilst 

 their central processes and the bodies of the columnar and 

 forked cells form the inferior layer of the epithelium. Peri- 

 pherie processes of the last-named cells, then penetrating 

 between the bodies of the goblet-cells, run straight outwards 

 to the surface of the gustatory disk (figs. 277 and 279). 



The goblet-cells (Kelch-zellen), the number of which upon 

 the larger papillae amounts to several hundreds, are prismatic 

 columnar structures, with five or six angles, caused by mutual 



