DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 5738 
thieren zur Ausbildung von bedeutend wenigeren, dafiir aber 
komplicierteren Zahnen benutzt wird” (3, p. 155). 
Concerning such a view we would remark that it amounts 
simply to a surrender of the idea of the fusion of morphological 
structures as such. The aggrandisement of one morphological 
structure at the expense of the material required for the deve- 
lopment of another, whereby the survivor is enabled to launch 
out into a further structural differentiation, may be a justifiable 
conception, but it ought not to be confused with a case of 
morphological concrescence. True morphological homo- 
logy deals with the identity of organic forms, not with that of 
the mere “ material” organised under such forms. In fact, 
it may be questioned whether the identity of organic 
material, as distinguished from that of the form 
under which it is organised, is at all a fruitful or even 
valid biological concept. 
In any case, until Kikenthal has disposed of the objection 
based upon the presence by the side of the molars (e.g. of 
Marsupials) of a residual lamina entirely comparable to that 
found beside other admittedly simple teeth, his theory of 
homology of the molars must be regarded as untenable. 
A still more fundamental question underlies the preceding 
discussion, i.e. whether the multicuspidate form of the modern 
mammalian molar has originated by the concrescence of several 
originally distinct and simple tooth-germs, or by the gradual 
evolution of cusps as outgrowths of a single simple conical 
tooth. 
In favour of the latter view are ranged the majority of 
paleontologists (cf. especially Cope [10] and Osborn [84]), 
who have elaborated a most plausible scheme showing the 
steps in the supposed evolution of the complex mammalian 
molars from a primitive conical type of tooth, through a very 
early tri-tubercular condition. 
The fusion theory, on the other hand, has taken shape chiefly 
at the hands of a few embryological investigators—notably 
Kikenthal and Rose. 
Rose has described the appearance, at a very early period 
