564 THE AMERICAN NATURALIST [Vol. LVI 



experimental material) can only be obtained by using 

 tliyroidectomized animals. 



Professor Henry Laurens, of the Department of Physi- 

 ology, informs me that several years ago he had a similar 

 experience with axolotls from New Mexico. He received 

 a shipment of several dozen in the spring, but was unable 

 to prevent them from transforming shortly after arrival 

 in New Haven. Only one animal of the lot failed to 

 metamorphose and was kept two years in the laboratory, 

 attaining a length of 14.25 inches. This individual was 

 used by the writer for thyroid transplantation work. 



The marked tendency of the New Mexican and other 

 American axolotls to metamorphose spontaneously when 

 moved from one locality to another prevents their being 

 used for aquarium purposes. It is an odd fact that prac- 

 tically the only axolotls used as aquarium material in the 

 United States are those that have been shipped from 

 Europe. 



The European strain seems to differ from the New 

 Mexican form in regard to spontaneous metamorphosis, 

 because these animals are handled by practically all 

 aquarium dealers in Germany and can be obtained for 

 a few cents apiece. Apparently they rarely spontane- 

 ously transform according to Jensen ('20), who has 

 worked extensively with this strain. The curious thing 

 about the New Mexican strain is that in their native 

 habitat they too may remain for considerable periods as 

 larva, yet when shipped from New Mexico to New Haven 

 promptly metamorphose regardless of size or age. One 

 large animal of this strain obtained by Professor Lau- 

 rens failed to transform and was kept in the laboratory 

 for two years ; at the end of this time it showed no indica- 

 tions of metamorphosis and was killed for thyroid trans- 

 plantation work. 



According to Gadow ( '08) the strain of axolotls estab- 

 lished in Europe came originally from the vicinity of 

 Mexico City. The first axolotls were brought to France 

 by Marshal Forey in 1863, and the present strain is de- 



