364 ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA. 



and Wallace have introduced it into science. Those naturalists dis- 

 tinguished by the word a gradual remodeling of the body, taking place 

 in the course of generations, corresponding to the new demands of new 

 conditions of life; in other words, the operation of natural selection, but 

 not a result from causes of variation suddenly and directly acting once 

 and in one generation. 



Just because the word " adaptation " may, according to customary 

 use of language, be used in many different senses, it would be desirable 

 to take it only in one acceptation and to have that fixed exactly; before 

 all, not to speak of adaptation when there is no mor2)hological chauge, but 

 only a sort of exchange of functions in Dohen's sense.* Thus, for exam- 

 ple, when FoKELt shows that fresh- water air-breathing snails, whose 

 organization is calculated for the direct breathing of the air, could 

 nevertheless pass to the greatest depths of the Alpine lakes, while they 

 used their lungs as gills. That with this not the slightest change has 

 taken place in the lungs, is shown by the observations of v. Siebold.l 



He saw the Pulraonates of shallow water use their lungs alternately 

 for direct air-breathing and for water breathing, according as the atmos- 

 pheric contents of the water was less or greater. If with v. Siebold one 

 should apply the word " adaptation " simply to such cases, it would 

 lose the special sense which was originally attached to it; as a technical 

 term the word would have to be given up. 



At any rate, there is as little a case of genuine adaptation in the Triton 

 *' larvae" that were capable of reproduction as in the Axolotl exception- 

 ally changing to the Amblystoma. In both cases, also, the transforma- 

 tion in consideration is not at all indispensable/or the life of the individual. 

 Mature Tritons (without gills) live, as I have witnessed, many months, 

 probably for years, in deep water, although they are fitted for simple 

 air-breathing; and Axolotls, asl have already stated above, can live quite 

 well for years in shallow and quiet water. If their gills shrivel, yes, 

 vanish entirely, this also yet is no adaptation in the Darwinian sense, but 

 a direct result of external influences, j^rincipally indeed of diminished use. 



A case quite analogous to Filippi's was observed in 18G9 by Jullien. 

 Four female larvae of Lissoiriton punciaftis Bell, (synonym for Triton 

 twniaius Schnd.) were fished out of a swamp and showed themselves 

 sexually mature. In their ovaries they had matured eggs, ready for 

 laying, and two of them also actually laid the eggs. Four male larvae, 

 which were taken in the same swamp, showed themselves likewise 

 developed in regard to bodily size, though they had no spermatozoa in 

 the testicles, but only sperm-producing cells.§ 



* " Der Ursprung der Wirbelthiere nnd das Princip des Functiouswechsels " (The 

 Origin of the Vertebrates aud the Principle of the Exchange of Functions). Lripsic, 

 18T5. 



t Faune profonde du lac Ldman ; Verhandl. d. Schweiz. Naturforsch, Gesellschaft 

 <Deep Fauna of Lake Geneva). Schafihausen, 1873, 



i Zeitschrift f. Wissenschaftl. Zool. (Journal of Scientific Zoology), bd. xxiii, 1873. 



■J Compt. Rend., t. Ixviii, p. 938, 939 (Proceedings of the French Academy of Sciences). 



