TONGUE OF ORNITHOBHYNOHUS PARADOXUS. 461 



without the use of a lens. The epithelium of the posterior 

 subregion is thus seen to be far denser and to possess an 

 obvious division into three layers, of which the median one is 

 much darker than the other two. The use of staining re- 

 agents and moderate powers shows far greater complexity, and 

 the various layers of cells behave very differently with different 

 reagents. Looking at many results it seems that there are 

 four distinct layers, best shown by aniline black and picro-car- 

 mine. Beginning from below the stratum Malpighii (I) 

 stains light slate colour in aniline black, light red in picrocar- 

 mine ; darker at the lowest layer of cells with both reagents. 

 The upper fusiform cells of the stratum Malpighii form a layer 

 (2) staining deeply in both fluids. Then follows a layer (3) of 

 very long thin cells whose outlines' are difficult to make out, 

 staining yellow in picrocarmine and straw-colour in Aniline 

 black. The uppermost layer (4) stains deeply for the most 

 part, and the outlines of the cells become distinct and the form 

 less attenuated except at the surface. Logwood gives the 

 same results, but in this case it is possible to see the nuclei of 

 the cells of layer 3, which ai*e usually long and thin, but 

 sometimes almost spherical, following the shape of the cells 

 themselves. In patches of variable extent the cells of layer 

 3 are continued into 4, not often reaching the surface. 

 The cells of layer 3 are shown by their behaviour with 

 reagents to be cornified, and the most remarkable thing about 

 the epithelium is the fact that in upward succession cornified 

 cells again become noncornified except in rare and isolated 

 spots. However, these cells are not cornified to the same 

 extent as those of the horny teeth and the papillae. This 

 epithelium is shown in figs. 6 and 7, and it is seen to be 

 thicker in the overhanging surface (fig. 7), where layer 4 con- 

 tains more cornified cells in larger patches. In all cases the 

 cornified layer (3) is continued upwards into the papillae of 

 the subregion, but corneous cells are also derived directly from 

 layer 4. Close to the point of transition into the anterior 

 subregion the cells above as well as below 3 stain especially 

 deeply, and at the junction itself 3 ceases altogether, while 



VOL. XSIII. NEW SER. H H 



