CHAPTERS ON EVOLUTION. 



grows in interest when we learn that in lower ranks of Vertebrate life, 

 groups of animals, separated apparently by the widest of intervals, 

 are now being linked together by the discovery of intermediate fossil 

 forms. The best-known example of the latter facts is found in the 

 relationship which may be now regarded as being clearly proved to 

 exist between reptiles and birds. Were we to search the whole 

 animal kingdom through for examples of creatures of thoroughly 

 different appearance, habits, and general conformation, no two 

 groups would fall more familiarly to hand than birds and reptiles. 

 There would, indeed, appear to be no similarity or likeness between 

 the secretary bird, which daily devours its quota of snakes, and 

 the prey upon which it lives ; or, reversing the comparison, betwixt 

 the unfortunate bird and the serpent whose stony gaze has allured 

 it literally to a living death. Activity of organisation on the one 

 hand would be opposed by a torpidity of action on the other ; 

 beauty of form and colour, by appearances frequently grotesque, 

 and often, in popular estimation at least, repulsive. The 

 contrast is one which, in the popular view, would be complete 

 and perfect in every respect. Birds are warm-blooded, and have 

 a four-chambered heart : reptiles possess a slow circulation, a low 

 blood-temperature, and a three-chambered heart, which, however, in 



the crocodiles becomes four- 

 chambered. The former class 

 is covered with feathers, the 

 latter with scales, bony plates, 

 or both. The fore-limbs, modi- 

 fied for flight in the bird, are 

 never thus used in reptiles 

 the so-called " flying lizards " 

 (Fig. 74) possessing no true 

 powers of flight, but being 

 enabled by a parachute-like 

 arrangement of their front ribs 

 to take flying leaps from tree to 

 tree. Birds, as we well know, 

 want teeth; and although in 

 tortoises and turtles, as typical 

 enough reptiles, a dental ap- 

 paratus is also wanting, the 

 reptilian character tends de- 

 cidedly towards a large and perfect display of teeth. 



A closer inspection and comparison of the skeletons of the two 

 groups, such as may be made in a very general review of their bony 

 possessions, would reveal several interesting points of likeness and 

 also of divergence. Thus both classes have a lower jaw which may 



FIG. 74. FLYING DRAGON. 



