282 Dr. W. Kiikenthal on ti 
that the double teeth represent an original condition, and are 
therefore to be regarded as molars, and further that CONICAL 
TEETH, WITH SINGLE TIPS, ARISE FROM MOLARS BY DIVISION. 
We have thus learnt a method by which numerous homodont 
teeth arise from a small number of heterodont molars. — I 
shall subsequently adduce the paleontological facts which 
substantiate such an origin of homodont from heterodont 
dentitions; I would here “only further allude in all brevity to 
an analogous phenomenon which occurs in a Bearded Seal 
(Phoca barbata) from Spitzbergen. 
Owing to mechanical causes (hard food, consisting of 
mussels, besides the final reason, which is the incomplete 
calcification of the teeth) the molars in the specimen before 
me have worn away, and, with the exception of the last, have 
cach become more or less completely separated into two, which 
present an absolutely similar appearance; instead of five molars, 
we consequently find seven and eight unicuspid teeth. 
The results of my embryological investigations decide the 
question whether the teeth of Whalebone Whales belong to the 
first or the second series, in so far as they show that rudi- 
ments of a second series of teeth are still present; the cord of 
epithelium in question is for the most part fused with the 
enamel-germ of the actual tooth, which therefore essentially 
corresponds to the first series. ‘he teeth belonging thereto 
resemble in this the so-called true molars of all other mammals, 
which, as they have no precursors in the milk-dentition, are 
assigned to the second series, although they must be regarded 
as having arisen from the fusion of the rudiments of both 
dentitions. (In the case of the first molar this is often still 
distinctly demonstrable ; it is to be seen with especial 
clearness in embryos of Spermophilus leptodactylus, for 
instance. ) 
I refer the peculiar transformations of the dentition in 
pelagic mammals, which have just been described, to mecha- 
nical causes, terninating with diminished calcification, which, 
as being necessary for the diminution of the specific gravity, 
is a phenomenon of very frequent occurrence in pelagic 
mammals, and, as has already been shown, also gave the 
first stimulus which led to the occurrence of hyperphalangy, 
as well as the loss of the dermal armature ot the Toothed 
Whales*. 
* In my paper on the “‘ Adaptation of Mammals to Aquatic Life ” (Zool. 
Jahrbiicher, 1890 [Ann. and Mag. loc. cit.]), I explained these views in 
greater detail. Of the former presence of a dermal armature in Toothed 
Whales, which I inferred from grounds of comparative anatomy and 
embryology (Anat. Anzeiger, 1890, p. 237), I am now able to adduce~ 
paleontological proofs also. 
