388 THE AMERICAN NATURALIST. [Vol. XXXVII. 



equally active in the same place ; their -ills were long and well 

 fringed ; not one showed the labored upward ascent or the dead 

 after-sinking which characterize the larva in which metamorpho- 

 sis has begun. Suddenly, within twenty-four hours, this air- 

 taking at the surface entirely ceased ; a half hour's watching 

 showed hardly a swirl. Yet the larva: were still there ; for a few 

 days later, the water being let from the basin, I caught them, 

 not one showing a trace of gill shrinkage. Experiment with 

 larva: under controlled conditions conclusively confirmed these 

 general observations. Moreover, larvae in metamorphosis do not 

 rise with especial frequency ; and times of rapid surface play 

 have never coincided with times of wholesale metamorphosis. 



It has been further said that, just as the bringing of Amblys- 

 toma into the air would force the change to the adult condition, 

 so enforced aquatic conditions would prolong the branchiate 

 condition, — larvae would not undergo metamorphosis if kept in 

 water and unable to crawl out, e. g., if kept in glass vessels with 

 perpendicular sides. Yet several hundred larva: have undergone 

 metamorphosis in my laboratory under precisely these conditions ; 

 not one, in fact, has refused to do so. The form of the aquarium, 

 the accessibility or inaccessibility of a foothold out of the water 

 have exerted no noticeable accelerating or retarding influence 

 upon the duration of the larval state. Indeed, I have thus far 

 been unable to raise larvae in the laboratory to their maximum 



many ways, and they thrive well, too well, as the sequel will 



while, in one instance, I have seen hundreds of larvae in a pond 

 that exceeded this dimension. Out-of-door experiments, in tanks, 

 cisterns, etc., have, with one exception, to be mentioned later, 

 led to precisely similar results. Larvae undergo metamorphosis 

 where the possibilities of terrestrial life are not present ; they 

 undergo metamorphosis under conditions where larvae flourish, 



The most crucial proof, it has been thought, of the power of 

 adaptive response in the young of Amblystoma has been the 

 bringing of the young into shallow water or out of the water 

 altogether, that enforced lung breathing might induce the transi- 



