1890.] z The Teeth as Evidence of Evolution. 231 
present teeth of quite contrasting appearance. Yet the ancestors 
of the animals whose teeth now so clearly separate them into the 
piscivorous, carnivorous, insectivorous, herbivorous and omniv- 
orous families, did not so widely diverge. The early Tertiary 
mammals, whether they were herbivorous or carnivorous, pos- 
sessed the full number of forty-four teeth, which appears to have 
been the typical number. While the present adult cud-chewing 
animals no longer possess the incisors and canines in the upper 
jaw, those ancient ruminating mammals, the Dicobune, Dichodon, 
and Anoplotherium, had incisors and canines in both upper and 
lower jaws. 
The elephant has the incisors of the lower jaw absent, the premo- 
lars absent, the true molars united into compound organs of great 
complexity, and the upper incisors developed into tusks, while its 
great prototype, the Dinotherium, possessed permanent premolars 
in both jaws, the true molars simple, and had the incisors in the 
lower jaw. ha F example is found in the bear of the present, 
which has the Wird true molar absent, while its ancestor, the 
Amphycyon, has the entire set intact. 
Evidence from Embryology and Rudimentary Organs—Prof. 
Goodsir has discovered that in the embryos of the modern rumi- 
nating mammals, calves, for instance, the rudiments of the canines 
and of the incisors of the upper jaw appear, but do not pass be- 
yond the rudimentary stage after birth. 
An organ which is not in use atrophies, and an animal which 
has no use for certain teeth loses them. Nature conserves, but 
- wastes not. 
The organs may be preserved in the embryos, because the 
embryo passes through all the stages through which the species 
passed in its evolution. 
In the whalebone whales there are varieties which have the 
full set of teeth germs to form during fetal life, and even to cal- 
cify, but become completely absorbed before birth; in others, 
where some of the teeth remain in the jaw, they are covered up 
by the gum during the entire life of the animal ; in others still, 
the teeth of the upper jaw alone are rudimentary and functionless, 
being imbedded in the gum. 
Am. Nat.— October,—2. 
