500 The American Naturalist. eer 
banded Armadillo most careful researches were made upon 
the dental ridge in a series of 420 sections, leading to a dis- 
covery which was confirmed in the other species, that the 
dentition of the Edentata has arisen by degeneration from the 
dentition of a more highly organized mammalian type. This 
result is directly contradictory to the hypothesis of Oldfield 
Thomas, that the Edentata were sharply marked off as Para- 
theria by the exceptionally simple features of their dentition 
among other characters. 
Dr. Röse continues, that the enamel of the teeth has so far 
retrogressed, that only an upper capping of the enamel layer 
is formed, which lies directly upon the dentine. “ In all cases 
in which we have instituted exact microscopical researches, in 
three species of Dasypus, and in Orycteropus, it is proved that 
invariably in the Edentata the typical two dentitions of the 
mammalia are exhibited in the embryonic stages. In every 
case as the tooth is constricted off, the dental ridge grows 
further backwards, as the basis of the successional tooth, as it 
has been observed in the development of the teeth in man and 
in the Opossum ; and as Kükenthal observes, from a morpho- 
logical standpoint it is of no moment whether this replacing 
ridge gives rise to teeth or not. ” 
Dr. Röse anticipates that the Bradypodide will also prove 
to be diphyodont. 
This author further shows that there are proofs of heterodonty 
which weigh against the opinions of Parker and Thomas, that 
the Edentata stand entirely aside from the other mammalia. 
In the early stages of development, a continuous dental ridge 
is found in the whole jaw, and in the anterior part of the jaw 
two rudimentary teeth are observed which must be regardet 
as incisors. According to Rheinhardt, the number of rudi- 
mentary incisors in the Nine-banded Armadillo is still greater 
(four). The lateral tooth in Bradypus may be either an 
incisor or canine. Dr. Röse agrees with Tomes and Osborn 
that the canine should be considered as the most anterior pre 
molar. Another question arises as to whether the posterior 
teeth of the Edentata are to be regarded as molars or 9% 
divided into molars and premolars. As Kiikenthal be 
