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SUMMARY OF CURRENT RESEARCHES RELATING TO 
the corresponding teeth which these have replaced would in ordinary 
terminology be called milk-teeth. But what is to be said of those teeth 
which persist without replacement, viz. — 
d. i. 3, d. jp. m. 2, m. 1-3 9 
d. i. 3, d. C., d. jp. m. 3, m. 1-3 ’ 
Morphologically these belong to the same series as the so-called milk- 
teeth. On at least some of them replacing teeth are represented by 
distinct bud-like enamel-germs with corresponding mesodermic thicken- 
ings. The so-called molars develope from the enamel ridge in precisely 
the same manner as the preceding milk-teeth. The hedgehog has a 
complete milk-dentition, but the replacement is less perfect than in most 
Placentalia, thus what persists is partly due to the first set, partly to 
the second. But in connection with the third upper incisor (d.i. 3) and 
some others, there are hints or residues of a still earlier generation of 
teeth, so that what we call the first and second set should be called 
second and third. Nor is the possibility of development exhausted in 
forming what is called the second set, for there are hints of yet another. 
The dentition of certain fossil Erinaceidse agrees with the first set rather 
than with the second. 
Omitting what the author says in regard to shrew and cat, we shall 
notice his interpretation of the marsupial dentition. He confirms some 
of Kukenthal’s work. The second set of teeth is represented by bud- 
like enamel-germs, partially surrounded by thickened connective-tissue, 
which at a certain stage are associated with all the teeth in front of the 
third molar. But of these germs only one, the third premolar, developes 
into a functional tooth. All the persistent teeth of marsupials, except 
the third premolar, correspond to those of the first set in Placentals. 
Reasons are given for believing that a complete second set never existed 
in Marsupials. 
In connection with Edentata, it is noted that in embryos of Tatusia 
peba there are rudiments of more teeth than do subsequently become 
calcified. The dentition of Dasypodidae is not strictly homodont ; only 
the first and eighth tooth are simple cones, those intervening (in the 
first set) have a median tubercle and a lower lateral one. In regard to 
Cetacea, the author states that the persistent dentition of toothed whales 
(all ?) corresponds to the first set in other Placentals. 
The teeth of the second set (replacing teeth) are not descendants of 
those of the first set (milk teeth), but develope lingual- wards to these 
direct from the enamel ridge. Reasons are given showing that the first 
set may be regarded as ontogenetically and phylogenetically the older. 
Four stages of dentition may be established : — 
(1) The persisting dentition consists wholly of the first set 
(Odontoceti). 
(2) The persisting dentition consists of the first set excepting the 
third premolar (Marsupials). 
(3) The persisting dentition consists of molars of the first set, 
w hile incisors, canines, and premolars are partly of the first and partly 
of the second set (Hedgehog). 
(4) The persisting dentition consists, excepting the molars, only of 
the elements of the second set (higher Mammals). 
