Morphological J^ariation and lis Causes in A. tigrinum 19 



how natural the aquatic Hfe is to the species, provided that the 

 perfect conditions therefor are present. My former impression 

 was that the permanent aquatic type was produced only by con- 

 tinuous nutrition at low levels. I have produced them thus in 

 cisterns, and I am now experimenting with such animals taken 

 from the lakes of high altitude in Colorado. They are undoubt- 

 edly of the species ligriiiniii, but are a dwarfed and stunted race, 

 though perfectly mature sexually. Such animals as these may 

 perhaps be spoken of as "larvae," which have been retarded in 

 development as the result of a "hemmung." But such ambly- 

 stomas as I have described above are animals of the most superb 

 development, despite the fact that under proper conditions they 

 may undoubtedly remain perfectly and permanently aquatic. 

 They outgrow all ordinary adults ; they breed naturally, females 

 depositing over a thousand eggs at the first spawning. And, as 

 I have indicated, they show delicate morphological as well as 

 color characters which classify them as perfect adult animals. It 

 is true they are subject, even after breeding, to the accident, the 

 fatality, of metamorphosis ; but neither this nor their analogy to 

 other larval forms makes them in any true sense of the word 

 "'larvae.'' In many if not in all respects they are the most highly 

 developed adults that the species is capable of producing. Much 

 less is there any scientific reason for designating, as has been pro- 

 posed, these sexually mature branchiate amblystomas as axolotls, 

 in distinction from the sexually immature branchiate, for which 

 the term "larva" is to be reserved. The popular term axolotl has 

 no scientific value, nor is it applied solely to sexually mature in- 

 dividuals of the species jn its Mexican habitat. And again I may 

 add that there is no gain, but much loss, in seeking to explain or 

 even to classify these phenomena by the use of the term "ne- 

 oteny." The use of this word "neoteny'' merely stereotypes with 

 a high sounding title a partial knowledge and a thoroughly false 

 interpretation of the facts. The only scientific mode of express- 

 ing the facts would be to speak of A. ti grin run as a dimorphic 

 species, possessing an aquatic as well as a terrestrial form. The 

 fact that the latter is developed only by passing through the for- 



21S 



