TITI>; TURTLE. 



119 



Additional Facts About tlic Turtle. 



Notwithstanding the very unlike appearance of 

 the pigeon and the turtle, an arrangement of their 

 resemblances shows that birds and reptiles are very 

 closely allied. So close is the relation between them 

 that Mr. Huxley puts Inrds and reptiles into one class, 

 which he calls Sauropsida. The resemblances are so 

 important that they seem explainable only on the hy- 

 pothesis that birds have descended fi'om some form of 

 Reptilia, although not from turtles or snakes. 



The most reptile-like or- ;• '^ 



ders of birds are extinct and ' 

 known only by their skele- 

 tons. The most liirdlike 

 orders of reptiles are also 

 extinct, so the living ])irds 

 and living reptiles are very un- 

 like each other. One of the 

 earliest birdlike forms tliat ever 

 existed is called the Arch;eop- 

 teryx. It has been found as a 

 fossil skeleton in some limestone 

 beds in Germany. The accompa- 

 nying hgiire shows how Mr. Shu- 

 feldt thinks it must have looked. 

 It is difhcult to decide whether 

 a creature like this should be 

 called a reptile or a Inrd. 



Tlie characteristic feature of the turtle is the shell. 

 This is composed of the vertebrae of the back, which 

 are solidified together ; of the expanded and con- 

 solidated ribs ; and of tlie exoskeleton, which, in the 

 turtle, is developed as horny plates and consolidated 

 with the internal skeleton. The vertebrae of the 

 pigeon's back are also consolidated, but for a different 



ATiCH.-EdPTERYX 

 (AFTER SHUFELDT). 



