CHORDATA — VERTEBRATA — AMPHIBIANS 349 



13. Define archipterygium. What is the probable relation 

 of this to the limbs of the higher vertebrates ? 



14. Sketch Semionotus in outline, with a small portion of 

 body in detail to show the rhombic scales. Label scale and 

 the various fins. To what order does it belong ? 



15. Sketch Diplomystus or Mallotus, noting fin-rays, vertebrae. 

 To what order does it belong ? 



Class D, Amphibia 



These differ from fish mainly as follows : they have paired five- 

 toed Umbs in place of paired fins ; each limb consists, as in all the 

 higher vertebrates, of one bone in its upper portion, two in the 

 lower portion, also several wrist or ankle bones and jointed fingers 

 or toes ; when a median fin is present, as in the tadpole, it lacks 

 fin-rays. Amphibians breathe by gills in the larval condition, but 

 usually by lungs in the adult. A cloaca is present. Skin usually 

 without scales; it is kept soft by the many mucus-secreting 

 glands, hence the animals breathe also through the skin. The 

 skeleton is ossified. The skull is flat and articulates with the 

 spinal column by two condyles. The ribs are short, not encir- 

 cling the thorax. Nearly all pass through a gill-breathing, tad- 

 pole stage before breathing by lungs. See page 353. 



The structure of amphibians is such that they could not adapt 

 themselves to dry air but could live in swamps and damp places 

 where fish could not live. In the order Stegocephalia they 

 tried to adapt themselves to a life upon dry ground but were 

 not very successful. 



Derivation of name. — Amphibia > Greek amphi, both, 4- 

 bios, fife. They are water-dwellers during one portion of their 

 lives, and land-dwellers during another portion. 



The Amphibia are divided into the following orders : -^ 



Page 



1. Stegocephalia 352 



2. Urodela (Caudata) 352 



3. Anura (Ecaudata) 353 



4. Gymnophiona , 354 



