410 MR. E. G. BOULBNGER ON THE 



Axolotls in shallow water, Stage 3 being reached on January 

 10th and 25th, and Stage 4, the stage when- the front part of the 

 fin becomes totally absorbed, on February 12th and 28th. The 

 Axolotls were then returned to deep water : the development at 

 this stage, however, could no longer be checked and both creatures 

 completed their metamorphosis in the water. 



From the latter experiment, showing that when replaced in 

 deep water the previous stages were resumed in about half the 

 time required to reach them, the conclusion may I think be 

 drawn that the natural tendency undoubtedly is for the animal 

 to remain an Axolotl, and that compulsion is needed to bring 

 about metamorphosis. 



It will be noted that at Stage 4, when the front part of the 

 fin becomes absorbed, the metamorphosis can no longer be checked, 

 and that this is therefore to be regarded as the critical stage, at 

 which the further development must proceed whatever the 

 conditions under which the animal is placed. 



During the covu^se of all my experiments, with the exception 

 of the last stages of the metamorphosis, the Axolotls fed with 

 regularity twice a week, and in this respect I experienced none 

 of Mile, de Chauvin's difficulties. 



Below will be found detailed accounts of the conditions under 

 which my eleven specimens wei'e kept, and of the changes which 

 took place under the circumstances. 



Specimen i\'o. 1. 



Placed in shallow water at a temperature of 75°-80°. 



Stage 1. August 17th. — Length 138 mm, 



,, 2. September 1st. 



,, 3. September 15th. 



„ 4. October 17th. 



„ 5. October 24th. 



,, 6. November 2nd. 



,, 7. November 8th. 



,, 8. November 14th. — Length 131 mm. 



Total length of period — 12 weeks. 



S'peci'men No. 2. 



Placed in shallow water at a, temperature of 75°-80'^. 



Stage!. August 17th. — Length 119 mm. 



., 2. September 1st. 



,, 3. September 15th. 



,, 4. November 9th. 



., 5. November 16th. 



,, 6. November 21st. 



„ 7. November 29th. 



,, 8. December 4th,— Length 113 mm. 



Total length of period— 15 weeks 



