154 THE STORY OF ANIMAL LIFE 



Amphibians that have Scales. These are very 

 minute, embedded in the skin, and arranged in 

 transverse rings. The name Gymnophiona, naked 

 serpents, is therefore doubly inapplicable: for 

 they are not serpents, and not scaleless. 



The Reptiles and Birds at first sight seem to 

 be widely different. The latter are the warmest 

 blooded of all vertebrates, the former are cold- 

 blooded. The one wear feathers, the other scales. 

 Nevertheless, there is an intimate connection be- 

 tween them ; the reader has doubtless already 

 learned from other sources the facts about their 

 relationship, so we will not here do more than re- 

 call a few of these facts. Ope is, that the birds 

 of earlier times had teeth in their beaks, and pos- 

 sessed jointed tails. Another, that the Reptiles 

 of earlier times included forms that were able to 

 fly. A third notable fact is the presence of claws 

 on the wings of some birds, showing that the 

 wing of the bird was not always wholly spe- 

 cialised for use in flight. 



We owe to Professor Huxley, the recognition 

 of the close relationship of Birds and Reptiles, 

 and the name Sauropsida (Reptile-like animals), 

 under which both are included. They agree in 

 being air-breathers and never having gills, except 

 the rudiments present in the early embryo: this 

 distinguishes them from Amphibia. They agree 

 in having the skull set on to the back-bone by a 

 single articulating surface or condyle; and thus 

 differ alike from Amphibia and from Vertebrata. 

 They agree in having the red corpuscles of the 

 blood nucleated ; and in this differ from the Mam- 

 malia, in which the red corpuscles are non- 

 nucleated discs. From a popular point of view, 

 we may say that the striking distinction between 



