408 THE AMERICAN NATURALIST. [Vol. XXXVII. 



largest larvae of the ordinary type which I have as yet seen. 

 The adults resulting from their metamorphosis are nearly as 

 distinct as are the young. They represent, in man)' features an 

 extreme development of what Cope has designated the " Western 

 form" of Amblystoma tigrinum. But, in the writer's vicinity, 

 they seem to constitute only a very small minority of the species, 

 not more than one out of several hundred. 



This form, as already indicated, seems to be very resistant to 

 metamorphosis; it has shown itself so under experiment; and, 

 in ponds where the ordinary form leaves the water at a very 

 small size, these occasional giants may continue in the larval state 

 until they have outgrown all but the very largest adult members 

 of the species. There is thus, in the case of these larvae, plainly 

 another factor present, in the retardation of metamorphosis. 

 And, as both the mature and the immature stages of this form 

 resemble, morphologically, the perennibranchiate types in several 

 respects, it seems, at present, natural to interpret them as rever- 

 sions toward a more primitive and perhaps perennibranchiate 



But although these giant, flat-headed larvae resist metaim <v\ >h< »is 

 without the especial retarding conditions which usually prevent 

 the change, yet it is to be noted that they, too, undergo meta- 

 morphosis in the water, and that high feeding, followed by 

 partial feeding or by starvation will apparently invariable bring 

 about the result. I have taken several giants in the early stages 

 of metamorphosis from deep water ; and all the specimens in my 

 possession have finally undergone metamorphosis in aquaria. 

 The branchial apparatus seems more resistant than usual ; the 

 whole process takes longer ; and the order in which the several 

 component changes occur is different ; but the physiological 

 aspect of the process, its causes, etc., remain the same, aside 

 from the matter of delay. 



A word, in conclusion, as to the significance and setting of 

 these facts in general theory. The writer does not, with 

 Weissmann, hold that the facts relative to the metamorphosis of 

 Amblystoma or the Axolotl mav be sufficient to settle cardinal 



one species can be conclusive, or, indeed, more than merely 



