179 
Partial Metamorphosis in Amblystoma mexicanum. 
SUMMARY. 
When metamorphosis of the axolotl has set in it may either 
progress till the animal concerned has assumed the amblystoma 
form or — provided a certain stage has not been surpassed — 
stop; in the latter case the animal living in normal conditions will 
reassume the original shape of the axolotl on regeneration of giils 
and dorso-caudal fins. Wintrebert 1 ) however described a case 
in which metamorphosis had stopped half-way and only been fol- 
lowed by a partial return to the axolotl-stage; for this reason the 
specimen was termed as a “demi-amblystome“. — The author has 
got possession of a similar, though not quite congruent case. 
An axolotl about three years old weighing 75 grammes on Oct., 
16.1919 was subjected to an intraabdominal injection of iodocasein. 
Signs of beginning metamorphosis were not observed until Nov., 
15.; thence forward it advanced quickly though displaying certain 
irregularities. In the middle of December the metamorphosis stop¬ 
ped altogether, and the animal has not changed its appearance 
from that moment till now. For a whole year afterwards it kept 
staying in the water basin, and it was not observed on land until 
December 1920. 
The demi-amblystoma concerned is, in accordance with the 
amblystoma-tvpe as regards the shape of the body, the absence of 
dorso-caudal fins, the presence of movable eyelids and the pro- 
perties of the skin. In distinction to these points of resemblance 
to the amblystoma the following features are like those of the 
axolotl, viz. the tall tai! compressed from side to side, the webbed 
hind feet, the retention of gili clefts and internal giil apparatus, the 
shape of the mouth, the palatine teeth and the tongue together with 
the colours of the skin covering the abdomen and the lateral super- 
ficies of the tail. The highly rudimentary external gilis resemble 
those characteristic of the latest stages of metamorphosis, when the 
gill-cleft is going to coalesce. 
In three other cases artificially enforced metamorphosis proved 
apt, as it seemed to stop at the same stage (viz. total resorption 
') Compt. Rend. Soc. de Biol. 1908. t. 2. pag. 415 & 549. 
12 * 
