DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES, 531 
the structure as an “‘ enamel-germ,” whether it develops further 
or not. 
With regard to the first of these two alleged guarantees 
of identity as genuine enamel-germs, it is held by the present 
writers that undue importance has been attached to the dis- 
tinction between the free end of the dental (residual) lamina 
while in the condition of a mere prolongation beyond the de- 
veloping enamel-organ, and the same prolongation when it has 
undergone some slight enlargement. With most writers, it is 
true, that distinction is not a very prominent one. Indeed, it 
would appear that, to the majority of them, practically any 
lingual prolongation of the dental lamina beyond its point of 
connection with a developing tooth is to be regarded as an 
“Krsatzleiste,” and therefore as the homologue of a suc- 
cessional tooth. In Kikenthal’s earliest reference to the 
marsupial condition (24) we find him basing his view of the 
“milk ” homology of the marsupial incisors upon the possession 
by them of an “Ersatzleiste” with a swollen (“kolbig’’) 
free end. On the other hand, neither Rose nor Woodward lay 
any particular stress upon the enlargement of the free end of the 
residual laminal downgrowth. They do not ignore its frequent 
occurrence, but neither do they seem to regard that feature as 
asine qua non of its title to consideration as an enamel- 
organ. The passage already quoted from Woodward (p. 525) 
will sufficiently bear out this statement as far as that writer is 
concerned. 
But according to Leche a mere lingual prolongation of the 
dental lamina beyond the point of attachment of the enamel- 
organ of a tooth gives of itself no certain promise of future 
tooth formation, or perhaps one should say, no reliable evi- 
dence of its morphological value as an enamel-organ of a 
succeeding tooth generation. Leche is thus forced to base a 
fundamental morphological distinction in large part upon that 
swollen (“kolben” or “knospenférmig”) character 
which is held to distinguish the residual dental lamina beside 
the teeth of Marsupials. It may be quite true that such 
thickening of the free end of the residual lamina is an invari- 
VoL. 39, PART 4,—NEW SER. 00 
