590 iin. M. F. WOODWA.ED ON [May 5, 



(6) The evidence advanced in support of the trituberciilar 



theory, is insufficient to prove that the upper molars 

 primarily evolved on the lines of that theory. 



(7) Owing to want of material, trituberculists have been led 



to assume that the upper molars of the early Mammalia 

 passed through similar stages to those which they have 

 determined for the lower teeth, and consequently they 

 have in most cases incorrectly identified the primary cone 

 (save in Peralestes and the living Centetidce and Ohryso- 

 chloris). 



(8) That as regards the primary cone, its ontogeny recapitu- 



lates its phylogeny. 



I do not mean to deny for one moment the occurrence of the 

 tritubercular type of upper molar tooth, nor even to underrate its 

 phylogenetic importance ; for no one who has studied cusp ontogeny 

 can fail to notice the frequency of its appearance, and the fact that 

 often (though not always) the three cones of the trigon are the 

 first to appear during development. What I desire to point out 

 is, that there is no evidence to show that this type of upper molar 

 arose in the way suggested by trituberculists, and that they have 

 in most cases overlooked the true primary cone. 



If the triconodont tooth be a stage in the evolutioQ of the mamma- 

 lian molar, then I should believe that the anterior cone disappeared, 

 the main cone becoming enlarged as the paracone and the posterior 

 one as the metaeone. At this stage the upper teeth overhang and 

 bite outside the lower molars, and the future antero-internal cone 

 (protocone) was developed as an internal shelf acting as a mortar for 

 the cusps of the lower teeth, and at a much later period developed 

 a cusp. The hypocone arose in a similar way with the elongation 

 of the teeth. 



The function and origin of the external cingulum with its 

 numerous cusps (2-4) is difficidt to understand, for in the living 

 Mole it is quite outside and free from all contact with the. lower 

 molars ; possibly it is of use to insect-feeding animals, giving them 

 greater hold of their slippery prey. 



In the Centetidce and Peralestes, the upper molars could not have 

 overhung the lower ones to the same extent, consequently no in- 

 ternal lobe bearing the protocone was developed and the external 

 cingulum was very largely developed. 



I have purposely left out all reference to the multituberculate 

 and concrescence theories, having restricted my researches to 

 endeavouring to ascertain whether the trituberculate theory respect- 

 ing the upper molars rested upon any solid basis, and whether one 

 of the molar cusps was more primitive in its mode of origin than 

 the others. 



Ontogenetically, I have failed to find any sup])orfc for the con- 

 crescence theory, neither do I consider that any of the evidence put 

 forward by Edse and Kiikenthal is at all conclusive in its favour. 



On comparing the several families which grouped together 



