Dcntiliun of Mammals. 283 



Kdkxtatks : embryos of Dasi/pus yiovrmcinctas ex[\\h\it[\Q 

 typical tbniiation of successors tor the tirst seven teeth; a 

 successor is waiitiiig- only in the case of" the last tooth. The 

 occurrence of tooth-change in this animal has already been 

 demonstrated by Tomes. IMoreover in the lower jaw of the 

 embryos I find not eight teeth, but eleven, of which the three 

 first arc smaller and do not cut the guin. 1 am now also 

 able to mention a second Edentate which lias rudiments of 

 two dentitions : i\\\s, \9, Dasypus villosiis. This phenomenon 

 consequently apj)ears to be of very general occurrence among 

 the arnjatlilloes. Whether actual tooth-change really takes 

 jilace is of no consequence for my purpose ; 1 merely affirm 

 the presence of rudiments of milk and second teeth. 



]\IarisupiALS : Flower, who was afterwards followed by 

 Thomas, bases his hypothesis that the milk-dentition is a 

 secondary acquisition on the ])art of the higher mammals, on 

 what takes })lace in JMareupials, in which either no tooth- 

 change or only the change of a third premolar occurs. The 

 dentition of AJarsupials is very generally assigned to the 

 second series, and the precursor of the third premolar regarded 

 as a milk-tooth. My own investigations upon this group 

 have so far extended only to the study of a series of young 

 specimens of Diddphiis of ditierent sizes. On the basis of 

 these investigations 1 assert that THE permanent set 01^ 

 TEETH IS TO BE ASSIGNED TO THE MILK, OR FIRST DENTITION, 

 and that only one second tooth, the subsequent third pre- 

 molar, occurs. I can easily iurnish the proof of this, as soon as 

 it is granted, that the two dentitions are also distinguishable 

 from the point of view of morphology, besides being so from 

 the physiological standpoint of the ditlerence in the time of 

 their appearance. The rudiments of the two dentitions, 

 which have a common origin in the primitive dental fold, are 

 so disposed, that the first set of teeth is developed from the 

 outer one, and the second from the inner. Kow my prepa- 

 rations show that this is the case not only in the third 

 premolar, but that the tooth-rudiments lying in front of it, 

 especially those of the incisors, also possess on the inner side, 

 branching off from the neck of the epithelial invagination, a 

 distinct twig of epithelium with a knobbed end ; and this 

 must be regarded as the earliest rudiment of the enamel-organ 

 of the second tooth. It at all events follows from this that 

 the entire dentition of the opossums is to be ascribed to the 

 tirst and not to the second series. The mainstay of the hypo- 

 thesis of Flower and Thomas, that the milk-dentition has 

 been secondarily acquired by the higher mammals, is thus 

 destroved. 



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