TONGUE OF OENITHORHYNOHUS PARADOXUS. 471 



the bulbs of Ornithorhynchus are, in their arrangement on the 

 summits of the ridges, more exposed than those of any other 

 animal. But this is made up for in one case by the sinking of 

 the whole ridge till it only communicates with the outside by a 

 deep and narrow chink (fig. 8), and in the other by the posi- 

 tion and relation to adjacent structures (fig. 10). 



The Origin of the Gustatory areas of Mammalia. — ■ 

 Omitting the fungiform papillse, which seem to be primarily 

 tactile (as they are here), and to have acquired bulbs compara- 

 tively recently — the gustatory areas are either of the circum- 

 vallate or foliate type. The former is by far the commoner 

 type, but foliate areas are not so rare as is generally supposed. 



They were first discovered in rodents, but there are indica- 

 tions of them in many orders, and I find them well developed 

 in Marsupials (I have found them in Phalangista with many 

 furrows whose sides were crowded with bulbs). Thus the two 

 types appear to have arisen together, as we find them both 

 represented in the lowest order in which they occur. It seems 

 to me that the ridges of Ornithorhynchus are intermediate 

 between the two. In both cases the bulbs become confined to 

 the sides (changing their mode of origin also) as the areas 

 become more exposed. A circumvallate papilla is then pro- 

 duced by the shortening of the ridge until it becomes a sub- 

 circular elevation. At first the base of the papilla would be 

 constricted as it now is in Perameles. Then the sides would 

 become straight, and the vallum very deep and narrow (Pha- 

 langista), and finally the vallum becomes wide and shallow 

 and of very little value for protection, as in most higher mam- 

 mals. Conversely the ridge lengthens, rises to the surface, 

 and two furrows of a foliate organ are produced, over both 

 sides of which the terminal organs would spread. Just as the 

 circumvallate papillre of marsupials present traces of this origin, 

 so their foliate organ (as far as I have seen it) consists of a 

 less number of furrows than other Mammalia, and with a less 

 regular arrangement. 



As a conclusion to these hypotheses, it is well to remember 

 that Ornithorhynchus cannot show us the exact ancestral form 



