Metamorphosis of Axolotls 
55 
■gills but, on the contrary, carries away their dissolved plasma. 
Increased metabolism caused by thyroidine may possibly affect 
first the gills, causing the dissolution of their tissues, when the 
other organs of the axolotl have suffered no loss. 
Kornfeld’s investigations on salamanders, as well as my own 
observations on normally fed axolotls, show that the gills of 
amphibians are the punctum minoris resistentiae. Kornfeld’s ex¬ 
periments show that every injury to the organism causes a transit¬ 
ory reduction of the gills:.... „wir können daraus entnehmen, daß 
die degenerative Rückbildung eine Erscheinung ist, mit der die 
Kiemen immer in gleicher Weise auf die verschiedenartigsten Schä¬ 
digungen reagieren“. 
The evolutionary state of gills in normally fed axolotls is sub¬ 
jected to considerable oscillations. Seemingly without cause, the 
gills of certain specimens become shorter than those of others 
living under same conditions. I found however that, in larvae with 
diminished gills, processes of regeneration of limbs occurred (which 
axolotls frequently bite off each other). It is probable that more 
abundant supply of nutritive substances to parts undergoing re¬ 
generation is connected with partial atrophy of the gills. 
Simultaneously with degeneration of gills resorption of the fin 
.-sets in. The fin is composed of loose connective tissue, containing 
numerous capillary vessels and is surrounded by a two- or three¬ 
layered flat epithelium. On dissections of the tail made near the 
body, we also find the dissected medulla (Fig. 9). The fin of an 
axolotl to which I gave four times 0 25 gr. of thyroidine during 
10 days, decreased by more than one-half (Fig. 10). This diminution 
is uniform, so that the proportions of the organ are preserved. 
The epithelium has undergone changes similar to those described 
in the epithelium of the skin. In the connective tissue many leuco¬ 
cytes appear, but it is difficult to decide whether any active rôle 
in the degeneration of tissues should be ascribed to them, since 
numerous aggregations of leucocytes are also found in the tail of 
.normally fed axolotls. 
In the structure of the gills as well as of the fin of axolotls 
fed on thyroidine, we are struck by the sudden decrease of volume 
of these organs. In microscopical dissections at this stage a more 
compact structure is observed (a larger number of cells on a giv- 
<en surface than is normally found) and macroscopically a flac- 
