July 31, 1885.] 



SCIENCE, 



91 



ment, it is possible to convert the aquatic axolotl, 

 breathing by means of gills, into the terrestrial Ara- 

 blystoma, which breathes by means of lungs. Indi- 

 vidual differences, however, came to light which 

 demanded further inquiry. This has accordingly 

 been carried out, and Miss von Chauvin now lays her 

 conclusions before the public in the Zeitschrift fiir 

 wissenschaftliche zoologie. 



It w-as soon found that younger specimens could 

 be more easily transformed than older ones; but even 

 among individuals of the same age great differences 

 came to light, depending upon the manner of treat- 

 ment. Thus axolotls can be more readily converted 

 into Amblystomas, if they are kept in water contain- 

 ing little air, and are thus compelled to come more 

 frequently to the surface, and to breathe with their 

 lungs. Others, kept in richly aerated water, obtained 

 a sufficiency of air through their gills, and were, in 

 consequence, less readily converted. It appeared, 

 further, that it is merely requisite to apply any exter- 

 nal compulsion towards transformation up to a certain 

 grade of development, and that, when this has been 

 reached, the animals arrive at the higher form with- 

 out any further interference. 



The point of time when the axolotl has arrived so 

 far in its metamorphosis as to have totally lost the 

 power of living in water does not coincide with the 

 absorption of the gills. On the contrary, the most 

 recent observations prove that the power of the axolotl 

 to live in water may, under certain circumstances, be 

 retained for a long time in individuals which have 

 become completely adapted to a terrestrial life, and 

 only disappears after the first moulting. Various ex- 

 periments with axolotls which had passed through 

 this stage proved indubitably that a return to their 

 former life had become impossible : they completed 

 their metamorphosis, even though all possible means 

 were taken for its prevention. On the other hand, 

 axolotls which had lived for months in damp moss, 

 and had breathed with their lungs but had not 

 changed their skins, felt completely at home as soon 

 as they were returned to the water. 



This surprising fact induced Miss von Chauvin to 

 institute further experiments on the adaptive power 

 of the axolotl, and in particular to attempt by suit- 

 able treatment a repeated transformation of these 

 creatures from the lower to the higher stage, and 

 thence back again to the lower. This interesting 

 experiment has, in fact, been carried out with a suc- 

 cessful result. 



Without entering upon an account of the means 

 and the precautions used, or a description of the vari- 

 ous stages of transformation, we pass at once to the 

 results. 



An axolotl lived altogether for three years and a 

 half. The first fifteen months it spent naturally, and 

 without any interference, in the water; its develop- 

 ment was then artificially accelerated, and in twelve 

 days it was transformed into a lung-breathing animal ; 

 it then lived on the land for fifteen and a half 

 months; it was next, during the lapse of six days, 

 brought back to the water, where it spent three and 

 a half months; in the space of eleven days it was 



again so modified that it could once more live on 

 the land, where it remained for rather more than six 

 months, up to its death. 



The power of adaptation to a change of medium 

 was so distinctly marked in this animal, and was 

 maintained for such a length of time, that Miss von 

 Chauvin instituted a further experiment with axo- 

 lotls, with the object of interrupting at pleasure the 

 metamorphosis of these creatures, and suspending it 

 for years, and subsequently testing their adaptability. 

 For this purpose, served five axolotls, each about six 

 and a half months old, in which the development of 

 the lungs was easily so far accelerated that they could 

 live on the land. At this stage the further metamor- 

 phosis was suspended by a low temperature, and by 

 being placed during the night in water. Nevertheless, 

 in one specimen there occurred quite unexpectedly, 

 after the lapse of fourteen months and twenty-two 

 days, the first moulting, followed by the further con- 

 version into the Amblystoma form. The four others 

 were kept, however, for three years and two months 

 in the state of suspended metamorphosis. After the 

 expiration of this time, the attempt was made to con- 

 vert two of them back into axolotls, while two others 

 were to pass on fully into the Amblystoma stage. 

 The result of this experiment was afiirmative. The 

 first two specimens reverted to axolotls : of the latter 

 two, one died, while the other became a perfect 

 Amblystoma. 



The three experimental subjects, whose metamor- 

 phosis was arrested on Nov. 8, 1879, were in good 

 health in October, 1884, in spite of the most arbitrary 

 interference with their natural course of develop- 

 ment. The Amblystoma was indeed smaller than 

 those which had been transformed previously; but it 

 was nevertheless very active and greedy, and quite 

 conveyed the impression of a healthy, well-developed 

 animal. In the two axolotls also, the arrest of the 

 metamorphosis remained without injurious conse- 

 quences. They are well developed, and feel quite at 

 home in their element. They can be distinguished 

 from normal axolotls merely by a somewhat smaller 

 size, and by a less luxuriant development of the 

 external gills. 



The results of these experiments show how ex- 

 ceedingly great is the influence of the surrounding 

 medium upon the organism of animals. Of the 

 most important agents, air, water, and heat, the last 

 possesses indubitably the greatest power over the 

 nature of the animal; and next after it comes the 

 character of the medium in which the animal is com- 

 pelled to live. The external conditions of life can 

 transform the nature of an animal either by a sudden 

 metamorphosis or by protracted action; but, in op- 

 position to all these external agencies, there stands a 

 powerful influence seated within the animal, and 

 acquired by inheritance, which can, indeed, be modi- 

 fied to a certain degree, but never entirely suppressed. 

 This circumstance explains both the many individual 

 fluctuations in the result upon perfectly identical 

 treatment, and the want of success of so many ex- 

 periments. 



Miss von Chauvin points out that the cases of 



