6o CHILDHOOD OF ANIMALS 



Mexican axolotl (Fig. 19). These animals occur in large numbers 

 in lakes near Mexico City, where they form an important article of 

 food. They are dark-coloured, tadpole-like creatures which when 

 fully grown are seven to nine inches in length, and possess a swim- 

 ming tail with a fringing fin above and below, with the usual two 

 pairs of limbs with fingers and toes, and with three pairs of gills 

 projecting from the sides of the neck. They are quite hardy, and 

 are familiar objects in aquaria in Europe, where they breed freely. 



They were supposed to belong to the division of batrachians which 

 are known as Perennibranchiata, as they retain their gills and the 

 aquatic habit throughout life. In 1865, however, some young 

 axolotls, bred in the Jardin des Plantes at Paris, gradually lost the 

 gills and the fin along the back and tail. The gill-shts closed up, 

 the head became broader, and the animals left the water perma- 

 nently. The black skin became blotched with spots and streaks 

 of yellow, and it was soon recognised that a metamorphosis had 

 taken place, that the axolotl was not an adult perennibranch, but 

 the larval form of a well-known salamander, Amblystoma tigrinum 

 (Fig. 19). A German lady, under the direction of two professors 

 at the University of Freiburg, proceeded to make a set of careful 

 experiments, and found that it was possible to induce young axolotls 



