PROFESSOR HUXLEY'S LECTURES. 



219 



they go, you will observe are in favor of evolution to this extent, that 

 they show that in former periods of the world's history creatures ex- 

 isted which overstepped the bounds of all existing classes and groups, 

 and tended to fill up the intervals which at present exist between 

 them. But we can go further than this. It is possible to fill up 

 the interval between birds and reptiles in a much more striking 

 manner. I do not think that this is to be done by looking upon 

 what are called the Pterodactyls as the intermediate form between 



Fig. 5. Pterodactylus Spectabilis. (Von Meyer.) 



birds and reptiles. Throughout the whole series of the mesozoic 

 rocks we meet with some exceedingly remarkable flying creatures, 

 some of which attain a great size, their wings having a span of 

 eighteen or twenty feet or more, and these are known as Ptero- 

 sauria, or Pterodactyls. We find these with a bird-like head and 

 neck, with a vertebral column sometimes terminated by a short and 

 sometimes by a long tail, and in which the bones of the skeleton 

 present one of the peculiarities which are often considered to be most 

 characteristic of birds that of having pneumatic cavities, which make 



