No. 43 8]. 



AMBLYSTOMA TIGRJNUM. 



reached a size that is quite unusual in the writer's vicinity. 

 These larva: were excessively fat, and so tame that, despite the 

 clear water, they could almost be taken in the hand. The 



there, and underwent metamorphosis! little if any sooner than 

 their relatives in the pond. The next larva; discovered in the 

 same summer, likewise in clear water, were so wary as almost to 

 defy my best efforts with the dipnet, and the excitement of those 

 taken was incessant, even during the usually sluggish period of 

 metamorphosis, which, in this case, followed immediate'} upon 

 their transference to the laboratory. Restless larva; have, indeed, 

 invariably, with me, undergone metamorphosis as the result of 

 capture and change of conditions. This exceptionally sudden 

 and rapid metamorphosis is no doubt due to the sudden katabolic 

 changes induced by the excessive activity. Even with larvae of 

 an intermediate degree of excitability, a portion of the individuals 

 usually metamorphose as the result of removal to new quarters, 

 if they have attained the dimensions, etc., which makes meta- 

 morphosis easy. And the writer has been able to discover no 

 reason applicable to all such cases, other than that the shock of 

 new conditions, checking or changing food supply a little, always 

 upsets the accustomed rhythm of bodily functions and thereby 

 opens the way for change. 



The facts thus far cited have, in the main, been instances of 

 acceleration of metamorphosis, but if their observation and inter- 

 pretation has been correct, it follows as a natural expectation 

 that facts of the opposite nature should be forthcoming. If a 

 rich food supply suddenly checked is the common cause of early 

 metamorphosis, then a moderate but constant food supply should 

 postpone metamorphosis, until a maximum larval size has been 

 attained, or perhaps postpone it indefinitely. The experimental 

 verification of this side of the proof has been far more difficult, 

 although final success has been reached in a few cases, and these 



