DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES, 537 
this point, but also by examination of Rése’s figures of his models 
of the developing dentition in Didelphys (11; cf. especially 
his fig. 12). In none of the stages there represented do we 
get any indication of “ bud-like” or partially isolated struc- 
tures arising from differentiation of the residual lamina, which 
is there quite clearly shown (cf. his figs. 12 and 15) as a con- 
tinuous band. It is true that the contour of the latter, whilst 
plain and fairly even in parts, is in other places crooked and 
irregular; but the latter condition is obviously attributable, 
chiefly if not entirely, to the overcrowding of the developing 
teeth (cf. especially the incisor region of his fig. 12). 
In Rése’s models of the early stages of the human dentition 
(9) there may be followed the process of formation of a residual 
dental lamina, which up to a certain point exhibits characters 
very similar to those we find in the case of the residual dental 
lamina of the marsupial jaw. But the structural similarity 
between the indifferent stage of the human residual lamina 
and that of Marsupials really yields no evidence either for or 
against their actual and strict homology. For Leche has 
clearly proved! that residual laminze may be developed by the 
side of the enamel-organs of the second (permanent) dentition 
of higher mammals. And indeed, as already pointed out, he has 
figured a residual laminar downgrowth by the side of the one 
undoubted successional marsupial tooth in Phascolarctus 
(figs. 76 and 77), an observation which we have to a large 
extent been able to confirm for Perameles (cf. p. 521 and 
fig. 74). 
It is, to say the least of it, very suggestive that just in 
Phascolarctus, where the deciduous premolar is very rudi- 
mentary, and where, therefore, we may suppose the formative 
activity of the dental lamina to be less exhausted than in other 
1 See especially his notes on the third incisor and canine of Hrinaceus (6) 
on pp. 25, 26 of his monograph (8), and his illustrative figures, 28—30. Cf. 
also fig. 74 showing residual lamina (“ Schmelzkeimahnliche”) beside 
p. 1 in Phoca; fig. 94 showing same in Desmodus; and fig. 97 showing a 
similar condition of residual lamina beside i2 of the same animal. Cf. also 
Marett Tims’ researches on the dentition of Canis (87). 
