THE CAUSES OF ACCELERATION AND RETARDA- 

 TION IN THE METAMORPHOSIS OF AMBLYSTOMA 

 TIGRINUM: A PRELIMINARY REPORT. 



During the past six seasons the writer has been collecting 

 facts on the metamorphosis of Amblvstoma tigrinum, both 

 by observation and by experiment. It is hoped to publish an 

 extended account latter ; but as relatively definite results have 

 already been reached, the interest of the subject seems to war- 

 rant the present publication of an outline, giving o nclusions 

 and something of the evidence from which they have been drawn. 



The extreme variability of our tiger salamander in regard to 

 the time at which it undergoes metamorphosis is well known. 

 Individuals may breed in the larval condition: witness the Mex- 

 ican Axolotl, which the concensus of scientific opinion has now 

 practically reduced to the rank of a sexually mature larva of our 



animal, even to sexual maturity. More striking than these facts, 

 however, are the anomalies of size which frequently occur. My 

 largest larva weighed, before the beginning of metamorphosis, 

 one hundred and thirty-six grams ; my smallest adult weighed 

 but three grams. Thus a larva may outweigh an adult in the 

 ratio of forty-five to one. The above mentioned giant larva, 

 while kept in an aquarium, ate daily, for about two weeks, at 

 least one fair sized adult Amblystoma of its own species; some 



piece of liver the size of a man's thumb. 



extremes of variation ? Those familiar with the literature of the 

 settled: favorable conditions for aquatic life are supposed to 



