334 



PRINCIPLES OF ANIMAL BIOLOGY 



fitness for the environment came about through changes in the animals 

 tliemselves, rather than through changes in the environment. The fan- 



FiG. 230 Skeleton of the armored dinosaur Sregosaurus. {Frotn LuWn Organic Evolution. 



Courtesy of Macmillan Co.) 



tastic forms and the huge size which the dinosaurs, for example, assumed 

 can hardly have been responses to factors in the environment. The 



Fig. 231. — Restoration of horned dinosaur Triceratops. (After Lull, from Schucheri's 



Hintorical Gtolooy, John Wiley and Sonn.) 



evolution of these reptiles was probably started and directed by forces 

 within the animals, independently of external conditions. What these 



