Metamorphosis of Axolotls 
33 
these differences are not essential. The essence of metamorphosis 
is common to both groups of amphibians; it consists in the trans¬ 
ition of aquatic into terrestrial (or at least amphibious) life and in 
the subsequent series of morphological and physiological changes 
connected therewith (chiefly the transformation of the respiratory 
and circulatory organs). The cause of these changes is certainly 
the same in Anura and in Urodela. As to the factors compelling 
the amphibians to leave their aquatic life, or as to the external and 
internal conditions regulating metamorphosis, these questions have 
repeatedly attracted the attention of many investigators; they also 
.are the subject of the present research. 
From the time when Chauvin succeeded in inducing axolotls 
to undergo metamorphosis, the problem of the conditions which cause 
either prolongation or shortening of larval life has become one of the 
most vexed questions of Biology. It is known that specimens of 
Amblystoma mexicanum Cope which inhabit the lakes in the neigh¬ 
bourhood of Mexico City, retain their larval form in natural condi¬ 
tions during life and even multiply in this form. It was observed 
in Paris that these axolotls sometimes spontaneously underwent 
metamorphosis. Chauvin induced these amphibians to assume ter- 
restriallife and studied the factors which shorten their larval stage. 
Black, not full-grown axolotls were put into an aquarium partly 
filled with water, so that the dorsal part of the animal was not 
covered by the liquid. Compelled to breath above the surface, they 
slowly lost their gills and fins and, after a time, when put on land, 
underwent total metamorphosis, when suitably fed, i. e. if they 
were able to endure the period of hunger which accompanies me¬ 
tamorphosis. 
Since the time of these experiments various investigators paid 
attention to the influence of external conditions on the duration of 
the larval stage. They noticed factors either accelerating or retarding 
metamorphosis. 
Almost all workers on metamorphosis of amphibians ascertained 
influence of food on the duration of larval life. Barfurth, 
Camerano, Gadow, Kämmerer found that abundant food 
causes prolongation of the larval stage' whilst scanty nourishment 
or even starvation accelerates metamorphosis; Bataillon and 
Tor nier, on the other hand, maintained that hunger stops the de¬ 
velopment of the larvae and retards metamorphosis. 
Bulletin III. B. Janvier—Mars. 
3 
