Morphological ]\^riation and Its Causes in A. tigrinuiu 67 



This brings me to a brief discussion of the most significant bit 

 of variation which I have found in the species, viz., the modifi- 

 cation of the teeth, more especially of the palatine teeth. It is 

 due, as I have demonstrated, solely to this habit of the capture 

 of large prey. I regret not being able at the present time to pub- 

 lish drawings sufficiently accurate to show the exact amount and 

 nature of the variation. But the best judges to whom I have 

 shown the specimens pronounce the variation to be at least of 

 generic value. And I question whether, in the entire family Am- 

 blystomidae, a more aberrant and remarkable dentition can be 

 found. Cope speaks of the teeth of the normal larva as consti- 

 tuting the "larval arch," and this describes fairly well the naked- 

 eye appearance of the delicate series of almost indistinguishable 

 points forming little more than a white line, a little removed 

 from, and running parallel to the series of the teeth in the upper 

 jaw. A closer scrutiny, however, reveals more than this. In all 

 larvae that I have examined the arch proves to be divided, or at 

 least constricted, at three points, at its apex and laterally at two 

 points nearly opposite the inner nares. These divisions, although 

 hardly noticeable in young larvae are, I think, always visible 

 under a lens. They divide the palatal teeth into four combs. A 

 good lens, moreover, shows that these combs differ in width, the 

 posterior being composed of a single series of teeth, although not 

 always arranged in a perfect line ; while the anterior combs, of 

 about the same length, are composed of more irregularly set 

 teeth, the number making up the breadth of the comb varying 

 from one to three. As already indicated, the size of these teeth 

 is very small, they being hardly, if at all, visible to the naked eye ; 

 and to this should be added the fact that the palatal ridges upon 

 which they are situated are also very slight. The entire structure 

 projects but little from the soft palate itself, and, in looking 

 straight into the mouth is, of course, wholly concealed by the 

 downward projection of the upper lip and jaw. 



In the young cannibal, even of but 10 cm., all these features 

 are changed. An hypertrophy and specialization have taken 

 place that are prodigious. The teeth no longer even suggest the 

 word "arch," for the separation of the four areas is complete, a 



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