404 MR. E. G. BOULENGEE ON THE 



them in large glass vessels which were so disposed and the 

 water, so restricted that at one spot only could they dive quite 

 under, while everywhere else they carae into contact with the 

 air. The water was then gradually reduced. Within a few 

 days a change took place, the creatures leaving the water in from 

 four to fourteen days, the complete metamorphosis following 

 about ten days later. Mile, de Chauvin (3) summarized her results 

 as follows : — " From what I have said, the correctness of the view 

 suggested by Weismann must be established, namely that most 

 Axolotl larvse, if not all, complete their meta,morphosis, if in the 

 first place they come out of the egg healthy and are properly 

 fed, and in the second place meet with arrangements which 

 force them to change from breathing under water to breathing 

 above water." 



Dr. J. H. Powers (4) at Doane College, Nebraska, has more 

 i-ecently conducted numerous experiments on the metamorphosis 

 of North American examples of the Axolotl, and he has come 

 to the conclusion that the metamorphosis is not due, as was 

 thought by Mile, de Chauvin, to a direct response to changes in 

 conditions of environment, compelling them to resort to aerial 

 respiration, but to checked nutrition, ai:id that a careful study of 

 Mile, de Chauvin's methods and results seems to cast a doubt 

 upon the conclusion that enforced air-breathing caused the 

 metamorphosis. The following is a passage from Dr. Powers's 

 paj)er on the subject of this lady's experiments : — " Fearing that 

 her charges would die, as indeed they sometimes did, she 

 always prepared them for the trying ordeal of metamorphosis by 

 raising the temperature of the water in which they were kept 

 and feeding to the maximum, for several days, to which she 

 ascribes no other importance than giving the animals increased 

 strength. The Axolotls were then brought immediately into 

 water sufficiently shallow as to force them, at least part of the 

 time, to breathe air. In this latter condition the experimenter 

 complains again and again that it was next to impossible to 

 induce the Axolotls to take any food whatever. Thus in these 

 experiments we have high feeding followed by practical starva- 

 tion, and it seems that no control experiments were instituted to 

 determine what the efiects of over and under nutrition might 

 have been with Axolotls still in abundance of water. Yet most 

 interesting is it to note that even the varying factors of nutrition 

 seem to have been wholly neglected in the final interpretation of 

 the results." 



Dr. Powers's field-notes show that metamorphosis occurs 

 rarely, if ever, as the result of enforced air-breathing through 

 the drying up of ponds, and that in spite of repeated search at 

 appropriate times and places, no Axolotls have been found trans- 

 forming on the mud of drying ponds. 



Dr. Gadow (5), who not long ago visited the lakes near Mexico 

 City in which this creature lives, and where it is said to retain its 

 branchiate conditionj has been able to refute the theories framed 



