DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 539 
keimen die von jener hervorgerufene Differenzirung im Meso- 
derm wieder ausgeglichen wird ” (8, p. 131). 
These quotations from Leche are sufficient to dispose of the 
claim that a mere dermal condensation around an epithelial 
downgrowth can give any reliable guarantee of its nature. 
Our own observations have fully convinced us of the worthless- 
ness of this feature as a test character. Connective-tissue 
condensation, in which the cells become flattened and con- 
centrically arranged around an epithelial downgrowth or 
enamel-organ, is beyond doubt simply the response to the 
stimulus supplied by the continued proliferative activity of 
the epithelium. Naturally such condensation will precede 
tooth formation, but it will also accompany every other con- 
tinued growth of the epithelial lamina to whatever cause it is 
due; and, as a matter of fact, it is most markedly seen around 
those proliferating epithelial masses or cell-nests which so 
frequently appear during the absorptive and retrogressive 
metamorphosis of the dental lamina. 
Even on the ground of his own admission, then, we may put 
aside as incompetent that test of the genuineness of an enamel- 
germ which Leche bases upon the presence or absence of a 
rudimentary tooth-sac. And there remains only the swollen 
(“kolbig” or “knospenférmig”’) character of the epi- 
thelial downgrowths of the dental lamina, already criticised 
at some length. 
That Leche should find it necessary to appeal to the “ con- 
stancy of occurrence,’ “sharply stamped character,” and 
* long persistence ” of the supposed successional germs seems 
to us to indicate some mistrust of the judgment founded upon 
their structural features. But if the latter are insufficient to 
suggest that theory of their homology which he espouses, we 
are at a loss to see how the theory can be strengthened by the 
appeal to the vague characteristics referred to. Nor have the 
characteristics themselves greatly impressed us. The struc- 
tures in question do, doubtless, “‘ constantly occur,” but they 
are no more “sharply stamped” in character than the fact of 
their mere existence would demand ; nor do they “ persist ” 
