The INSECTIVORA are diphyodont and heterodont, having well-developed rooted teeth. The canines are usually weak, the incisors pointed, and those of the two jaws often meet like a pair of forceps. The crowns of the molars are characteristically studded with short cusps. Some genera, such as _Gymnura_ and the mole, _Talpa_, have the regular mammalian dentition. In the hedgehog, _Erinaceus_, the dentition is _i_ 3/2 _c_ 1/1 _pm_ 3/2 _m_ 3/3, total 36. In the genus _Sorex_ (Shrews) the teeth differ in the following two marked respects from those of most other Monodelphia, (1) they are monophyodont, (2) the lower incisors sometimes become fused to the jaws. Most Insectivora have square molar teeth, but in _Potamogale_, _Chrysochloris_, _Solenodon_ and the Centetidae the molar teeth are triangular in section. Four molars occur in _Centetes_. In the aberrant genus _Galeopithecus_ the dentition is _i_ 2/3 _c_ 1/1 _pm_ 2/2 _m_ 3/3, total 34. The upper incisors are placed at some distance from the anterior end of the jaw, and the outer upper incisors and canines of both jaws have two roots,--a very unusual character. The lower incisors are deeply grooved or pectinated in the same way as are the lower incisors of _Procavia_. The upper incisors and canines of both jaws bear many cusps, and are very similar in appearance to the cheek teeth of some Seals. The dentition of the CHIROPTERA is diphyodont and heterodont, and the dental formula never exceeds _i_ 2/3 _c_ 1/1 pm 3/3 _m_ 3/3, total 38. The milk teeth are very slender and have sharp recurved cusps; they are quite unlike the permanent teeth. The permanent teeth are of two types. In the Insectivorous forms the molar teeth are cusped, and resemble those of Insectivora. In the blood-sucking Vampire bat _Desmodus_, the teeth are peculiarly modified; the canines and the single pair of upper incisors are much enlarged and exceedingly sharp, while all the other teeth are much reduced in size. In the Frugivorous bats the molar teeth have nearly always smooth crowns. The dental formula in the chief genus _Pteropus_ is _i_ 2/2 _c_ 1/1 _pm_ 3/3 _m_ 2/3, total 34. The PRIMATES have a diphyodont and heterodont dentition, generally of an omnivorous type, with cheek teeth adapted for grinding. The incisors are generally 2/2, and the molars, except in the Hapalidae, are 3/3. In the Lemurs the upper canines are large, and the lower incisors slender and directed almost horizontally forwards. The Aye Aye, _Chiromys_, has the following singular dentition: _i_ 1/1 _c_ 0/0 _pm_ 1/0 _m_ 3/3, total 18. The incisors much resemble those of rodents having persistent pulps, and enamel only on the anterior face. In Man and in the Anthropoid and Old World Apes the dental formula is always _i_ 2/2 _c_ 1/1 _pm_ 2/2 _m_ 3/3, total 32.