ox THE METAMORPHOSIS 01^ THE AXOLOTL. 403 



31. Experiments on the Metamorphosis oE the Mexican 

 Axolotl (^AmJdt/ stoma tigriniini), conducted in the 

 iSociety's Gardens. By E. G. Boulenger, F.Z.S., 

 C*nrator of Reptiles. 



[Received and Read May 20, 1913.] 

 (Text-figures 75 & 76.) 



During the past year I have been experimenting on points relat- 

 ing to the metamorphosis of the Mexican Axolotl [Amblystoma 

 tigrinuin), and have succeeded in obtaining the transformation of 

 a number of specimens. This paper deals with the methods 

 employed, and gives a detailed account of the external changes 

 undergone by the animal during the process, a subject which, 

 Avith the exception of Dumeril's (1) brief account, has not, so far 

 as I am aware, been previously treated. 



Before describing my experiments, it may not be out of place 

 to give a short account of the history of the animal. Although 

 suspected by Ouvier to be but the larva of some unknown air- 

 breathing salamander or newt, the Axolotl of Mexico was 

 considered for many years to be one of the Perennibranchiata, 

 such fts Froteus, jVecturits, and Swen. In the year 1863 a number 

 of specimens were imported from Mexico to France, where some, 

 kept in the Jardin des Plantes in Paris, bred, and the young were 

 successfully reared. The conclusion was not uniraturally drawn, 

 that the Axolotl, having bred in the branchiate condition, could 

 not possibly be anything but a perfect aquatic animal. It was, 

 not, however, until over two years later that the subject assumed 

 a different aspect, for some individuals of the second generation 

 lost their gills and the dermal folds of the back and tail, developed 

 eyelids, and yellow spots on the skin, and taking to land, changed 

 into a land salamander, already well known from North America 

 as Amhlystoma tigrinwm. 



A few years later Weismann (2) tried to solve the question 

 as to whether it were possible to force the larvpe, if brought into 

 conditions which rendered the use of the gills difficult and that 

 of the lungs easy, to change into Amblystomes, and he therefore 

 experimented with several broods which were placed in shallow 

 water, and thus compelled to bi-eathe air more frequently. 

 Although he met with no success Weismann was not discouraged, 

 and came to the conclusion that the failure of his experiments was 

 due to his having been unable to bestow the necessaiy care and 

 attention on the animals : he therefore asked Mile, cle Chauvin, 

 a lady who had already done much careful experimental woi-k, 

 to take a" number of larvae, just out of the egg. rear them, and 

 make an attempt to bring them to the perfect condition. When 

 the Axoilot.ls were about 6 months old. Mile, de Chauvin placed 



Proc. Zool. Soc— 1913, No. XXYIII. 28 



