344 
The Mexican Axolotl , &c., 
Jane, 
The three experimental subjects whose metamorphosis 
was arrested on November 8, 1879, were in good health in 
October, 1884, in spite of the most arbitrary interference 
with their natural course of development. The Amblystoma 
was indeed smaller than those which had been transformed 
previously, but it was, nevertheless, very adtive 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 consequences. 
They are well developed and feel quite at home in their ele- 
ment. 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 exceedingly 
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 protradted adtion. But in opposition to all these ex- 
ternal agencies there stands a powerful influence seated 
within the animal and acquired by inheritance which can, 
indeed, be modified -to a certain degree but never entirely 
suppressed. This circumstance explains both the many 
individual fluctuations in the results upon perfectly identical 
treatment and the want of success of so many experiments. 
Miss von Chauvin points out that the cases of “ neotenism” 
(persistence of embryonal forms) recently observed among 
the Urodela find at least a partial explanation in the artifi- 
cial transformations of the axolotl as here described. For 
it has been shown that the tendency to continued develop- 
ment can be suppressed by suitable influences, and such 
influences may. make their appearances naturally and in- 
volve a persistence of the larval condition. 
The importance of this series of investigations on the 
primitive transit of the vertebrates from the water to the 
land has been already pointed out. It must not be forgotten 
that the remarkable tenacity of life of the amphibians is a 
capital element, both in such natural transit and in the suc- 
cessful result of the experiments described. With inserts 
the case is very different : their metamorphosis has, in certain 
cases, been suspended, both naturally and experimentally. 
But all attempts which we have made to induce the rever- 
sion of an insert to a larval condition have so far miscarried. 
