548 General Notes. 
over those portions of the tooth covered by true enamel, while at 
the apices of the cross crests the enamel organ had suffered degen- 
eration of its inner columnar layer and apparently also the reticu- 
lar portion, as a result of which the organ, just over the crests, had 
acquired the character of a stratified squamous epithelium. Here 
and there ragged masses of this tissue seemed to project into 
the surrounding tissues of the mucous membrane, as if dragged out 
of place by the gliding of the crowns of these young molar teeth of 
opposite jaws over each other. These results were obtained from a 
study of longitudinal sections of recently born rats, with the eye- 
lids still closed, but with the incisors just breaking through the 
ums. 
The great value which the present reviewer attaches to Dr. 
Von Brunn’s earlier observations does not lie in the new histologi- 
cal relations established, but in the discovery that the enamel 0 
the cross-crests of the crowns of the molars fails to develop in the 
embryo in a situation corresponding to the point where abrasion in 
the adult through use has slowly worn away this enamel covering 
-and exposed the dentine underneath. This mutilation (for such it 
is, although produced by an exceedingly slow process of wear), has 
very clearly been transmitted through heredity. That Dr. Von 
Brunn should have failed to draw this conclusion from his facts 
is somewhat surprising, and while glad to call attention to his very 
important observations, the present writer is of the opinion that 
these discoveries are amongst the most important made during the 
resent decade as throwing new light upon the method of the evo- 
lution of organisms. i 
Ina second memoir! Dr. Von Brunn continues his investiga- 
tions, and adds greatly to his preceding observations. He finds, 1m 
act, that in still earlier stages of the enamel organs of the several 
kinds of teeth are not different from those normally observed im 
other mammals, as shown by the tooth germs of the incisors of a 
uterine embryo of the rat 28 mm. in length. The enamel pea 
` in this last instance are simply cap or dome-like bodies, in w ich 
there is as yet no differentiation of the anterior wall as the perma- 
nent enamel germ of the enamel band on the anterior face of the 
incisors of the adult. This is clear proof that profound changes 
must be suffered by the enamel organ from its earliest appearance 
until its full differentiation, portions of which evidently must later 
become either functionless or acquire a new or m ified function. 
This is just what Von Brunn’s later researches most conclusively 
prove. They show, in fact, that in the rat the enamel osmi Pi 
comes functionless across the transverse crests of the molars a 
eruption, thus leaving the tooth to erupt with its dentine pe 
ered at those points. The remainder of the enamel organ Wat 
1 ie Au; shmelzorganes und Seine Bedeutung 
fir Ue gakbtidung. Arch, £ mik Annie RETX, HiS Dp Soro 
pls. XXI-II, Bonn. 1887. Bae! 
