Dentition of Didelphys. 291 
the dental rudiment and has a more or less distinctly swollen 
termination. The canine which follows has already attained 
a considerable size ; nothing more than remains of an epithelial 
cord lying on the inner side of it is still to be seen. Its base 
has still not entirely disappeared from the frontal sections, 
when the rudiment of the first premolar is already visible 
above it. The latter also exhibits on the inner side a cord of 
epithelium with a rounded end running from the neck of the 
enamel-organ. It was in vain that I sought in the gap, 
which occurs between this premolar and the one immediately 
following, for a possible tooth-rudiment which had disappeared, 
the existence of which has been rendered so probable by 
Thomas’s investigations: | found nothing whatever; on the 
contrary, the gap appeared to be relatively smaller than in 
the adult. The second premolar, which comes next (which 
is therefore the third according to Thomas), did not show the 
looked-for cord of epithelium, which only appeared again 
beside the third premolar. The dental rudiment itself is 
already well developed in all parts ; the epithelial cord lying 
on the inner side of it ends in a knobbed swelling of consider- 
able size. ‘This concludes the investigation of the premolars ; 
the next sections show us the conditions in the case of 
the molars. I was very much astonished when I saw inter- 
nally to the rudiment of the first molar also, a short but 
distinct cord of epithelium running close beneath the epithe- 
lium of the cavity of the mouth, and still more so when the 
second molar also exhibited a similar epithelial cord. The 
conditions here were very distinct: the short and somewhat 
bent neck of the epithelium of the enamel-germ gave off on 
the inner side a lateral cord, which was of tolerable length 
and which thickened at the end laterally, on the inside of the 
dental rudiment, into a knobhed swelling of considerable size, 
precisely as we saw in the case of the third premolar. In 
connexion with this attention must also be directed to the 
following points :—The lateral knob of epithelium lies at a 
tolerable distance on the inside of the rudiment of the second 
molar, which has already completely developed its separate 
cusps; these have the same number and arrangement as in 
the adult animal. Moreover, the epithelial knob is absolutely 
lateral and not posterior in position: it has already disappeared 
in sections in which the rudiment of the second molar is still 
distinctly present. Rudiments of teeth beyond the second 
molar are not yet to be found. 
I am now able to furnish abundant confirmation of the 
foregoing results, in consequence of the examination of two 
stages somewhat more advanced in development and measuring 
