382 
ME. CHAELES S. TOMES ON THE DEVELOPMENT AND 
Fig. 12. — A diagram constructed from a comparison of many longitudinal sections. An inspection of this 
serves to explain why figs. T & 2 show in transverse section as many as ten teeth, while sections nearer 
the base, e. g. figs. 3 & 4, show but four and two teeth respectively. 
layer of formed dentine, and outside this comes a continuous layer of enamel-cells 
(internal epithelium of the enamel-organ). A little later on, as the tooth-germ elon- 
gates, a shallow depression appears on the one side (fig. 8) into which the layer of 
enamel-cells runs without break ; the groove deepens, but at first the enamel-cells do 
not undergo any modification (see fig. 7) in that groove which is to become the canal 
for the conveyance of the poison. 
But at a later stage, when the crescentic pulp, with its layer of formed dentine around 
it, has arched round so that its extremities are approximating (fig. 9), a most remark- 
able change has taken place in that part of the enamel-organ which lines the groove. 
No distinct layer of enamel-cells can any longer be traced, but the whole space included 
in the concavity of the crescent is occupied by a mass of branched cells, which in their 
general aspect strongly recall the stellate tissue or reticulum which forms so large a part 
of mammalian enamel-organs. And as it is beyond all question that the enamel-organ, 
destined to play no active part in this concavity or canal, has become transformed into 
a sort of stellate tissue, are we to regard the stellate tissue of a mammalian enamel-organ 
as a retrograde metamorphosis of a superfluous tissue 1 Before becoming acquainted 
with the enamel-organ of a poison-fang I was aware, and had expressed an opinion, that 
the stellate tissue was quite non-essential, for there are many enamel-organs which form 
enamel of perfect structure and appreciable thickness which have never possessed any 
parts save their external and internal epithelium. 
Ultimately this stellate tissue seems to wither up and leave the canal empty, so that 
we must regard it, in this place at all events, as a step on the way towards the disap- 
pearance of the enamel-cells ; and as it is hardly to be found in advance of the thin 
edge of calcified dentine, it does little more than fill a void. A thin layer of enamel is 
formed round the exterior of a poison-fang ; but after what has been said, I need hardly 
say that no enamel lines the interior of the poison-canal. 
