TOOTH-GENESIS IN THE CAVIIDA. 265 
corresponds with the first cheek-tooth of my specimen, except 
that he mentions and figures a lingual downgrowth only, whereas 
in mine both lingual and labial downgrowths were present in the 
upper jaw, but only the former in the lower. This point is, I 
think, worthy of mention, for the reason that I have already [22] 
expressed my adherence to the current belief that the upper jaw 
retains the more primitive condition. In neither of these cases 
is the labial downgrowth present in the lower jaw, while in the 
upper it is present in the one case and not in the other. The 
conclusion appears to me to be that this labial downgrowth has 
already ceased to exist in the lower jaw, while in the upper jaw 
it is in the process of disappearance. The lingual downgrowth 
is present in both upper and lower jaws in Adloff’s specimen as 
well as in my own. In this I think one may find further con- 
firmation of the view that the dentitions present in the Mammalia 
tend to disappear from without inwards. 
Adloff makes no mention of any indication of the incisors, 
which are well marked in my specimen. He also says that m.1 
and m.2 were not yet to be found; whereas m.1 was present 
in mine as a flask-shaped non-invaginated mass, m.2 not being 
indicated. Possibly mine may have been a slightly older speci- 
men, which would not invalidate, but rather strengthen, the 
deductions I have drawn. 
Stage 2. Circumferential head-length ...... 2°7 cm. 
body-length ....... 7°5 em. 
99 
Reconstructed diagram of Stage 2. pi., permanent incisor; ppm., permanent 
premolar; dm., deciduous molar; m!, first molar; m°, second molar ; 
m, third molar ; 0.c., ‘‘ concentric epithelial bodies.” 
The incisors are now teeth of considerable size and curve back- 
wards deeply in the substance of the jaw. They are well-calcified, 
