240 



GENETICS 



gills, a tail flattened sidewise, for swimming, and other 

 features that fit it for living in the water. It lives in the 

 water thus all its life, becomes mature, produces eggs and 

 young; there it dies; it is never anything but an axolotl. 

 But if it is fed on thyroid, it undergoes a transformation 



B 



Figure 48. Axolotl (A), and Amblystoma (B), to show the dif- 

 ference in form and structure. Figures modified from those in 

 Brehm's Thierleben (19 1 2). 



comparable to that which changes a tadpole into a frog. 

 It loses its gills; its body form becomes greatly changed, 

 its tail is no longer flattened sidewise. It becomes fitted for 

 living on land, crawls out on the land, and is the creature 

 known as Amblystoma (figure 48, B). It now lives all the 

 rest of its life under this guise, as a land animal; it be- 

 comes mature in this condition, producing eggs and young. 



