396 THE AMERICAN NATURALIST. [Vol. XXXVII. 



from a reservoir where they had grown in pure, deep water, to a 

 single aquarium. Here they lived and throve, although the 

 oxygen of the water was so exhausted that minnows died in a 

 few minutes of asphyxia. Yet the gills of these larvae remained 



If metamorphosis really were caused by enforced aerial res- 

 piration, and if loss of branchial surface were a chief factor in 

 the process, both of which are assumed by the common hypoth- 

 esis, then it would seem to follow as a natural or even necessary 

 conclusion, that cutting off the gills should stimulate to meta- 

 morphosis. True, European experimenters on the supposed 

 Axolotl did not find this to be the case ; but their failure was 

 explained by the fact that the gills of the Axolotl were quickly 

 reproduced. Besides, the larva: experimented upon in Europe 

 were resistent to metamorphosis under most conditions. Gill- 

 amputation may have constituted a real stimulus to metamor- 

 phosis, and yet one insufficient to bring about the actual change. 

 It seemed to me that our larvae were much more favorable for 

 the experiment, for they are, most of them, predisposed to early 

 metamorphosis. And, moreover, I have not found that the gills 

 were reproduced with especial facility ; weeks may intervene 

 with but little growth, and no specimen in my aquaria has 

 reproduced a gill of normal type ; they remain short and 



