DISTANT RELATIONS. 103 



followed suit, so as to prevent confusion in 

 the brain between the two sides of the body ; 

 while the nose, which stands in the centre of 

 the face, was under no liability to such error, 

 and therefore still keeps up its primitive 

 direct arrangement. 



It is worth noting, too, that these tad- 

 poles, like all other very low vertebrates, are 

 mud-haunters ; and the most primitive among 

 adult vertebrates are still cartilaginous mud- 

 fish. Not much is known geologically about 

 the predecessors of frogs ; the tailless am- 

 phibians are late arrivals upon earth, and it 

 may seem curious, therefore, that they should 

 recall in so many ways the earliest ancestral 

 type. The reason doubtless is because they 

 are so much given to larval development. 

 Some ancestors of theirs primaeval newts or 

 salamanders must have gone on for count- 

 less centuries improving themselves in their 

 adult shape from age to age, yet bringing all 

 their young into the world from the egg, as 

 mere mud-fish still, in much the same state 



