LECT. II.] THE AXOLOTL. 29 



I am purposely forgetting, for the time, the slow accre- 

 tion of minute variations, taking place through countless 

 ages of time, and am considering sudden, per saltum, 

 transformations. Whenever and wherever it became 

 necessary that higher tracts of the drying surface of the 

 earth should be peopled with semi-terrestrial and terres- 

 trial forms, then I suppose these leaps of life to have 

 taken' place. The morphological force the indwelling 

 spirit of protoplasm actually did perform these wonders ; 

 thus we have still living in abundance, reptiles that 

 crawl upon the earth, mammals that march or gallop over 

 it, and fowls that fly in the open firmament of heaven. 



I do not, of course, forget that the few existing 

 Dipnoi the Ceratodus and his companions are settled 

 in their low estate, at their own height, on their own 

 morphological platform, and that there is little likeli- 

 hood of their undergoing any further metamorphosis, 

 now. Still, with the Axolotl 1 staring me in the face, 

 I cannot suppose even that to be impossible. But when 

 I imagine double-breathing fishes undergoing metamor- 

 phosis in the olden times, I am thinking of more simple 

 and archaic Dipnoi than even the Ceratodus or the 

 Protopterus of the present day. 



Every biologist knows that some types have persisted 

 in a low estate with little modification, others in a low 

 estate with much specialisation ; whilst other types have 



1 That large Mexican Salamander generally continues in a low larval state 

 throughout life, but now and then it becomes transformed, loses its gills, and 

 becomes a member of a higher family. 



