19 



transformation. The full-grown Frogs and Toads are of all 

 Yertebrates the most absolutely taillest. Hence they are called 

 Anura ; that is, " without tails." 



There is a remarkable fact about these temporary tails. The 

 notochord in them remains, without any ossification, as if it were 

 not worth while to grow them ; whereas in the permanently tailed 

 amphibians, such as the efts, tlie bony spine extends along the 

 tail. 



In Reptiles the tail is very often massive, and clearly a continuation 

 of the trunk ; still being used as a swimming or wriggling organ. 

 Some kinds of lizards, when seized by the tail, throw it off ; or 

 rather, it is broken off by violent muscular action. Our common 

 Lizard, and also the Slow-worm, have this habit. It has been 

 thought to be useful to the animal ; inasmuch as the violent 

 wriggling of the loose tail may attract attention, while the body 

 runs away. 



Some lizards, as the one called Basilisk, have a crest on the 

 I)ack and on the tail. The tendency to the formation of this may 

 possibly bo inherited from their amphibian or fish-like ancestors, 

 ■which had a dorsal fin. 



A prehensile or grasping tail is found in the Chameleon tribe, 

 and in many snakes. The Slow-worm has a tendency that way. 

 On the other hand, the Tortoises have comparatively short tails. 



Perhaps the most singular modification in Eeptiles is the rattle 

 of the rattle-snakes. This consists of several loose rings of skin, 

 and is sounded by shaking the end of the tail. There is a 

 rudiment of it in some other snakes. 



One kind, that has no rattle, was observed by Darwin, shaking its 

 tail like a true rattle- snake, so as to make a noise by striking 

 •against the grass, &c. This gives us some clue as to the way in 

 which the rattle may have originated. As to its use, it has been 

 suggested that the sound may serve to warn predacious animals of 

 the dangerous nature of their intended victim, and so save it from 

 attack. 



From the Reptiles let us pass to their modified relatives, tlie 

 Birds. Although the modern bird's tail is the greatest possible 

 contrast to the long scaly one of the lizard, yet one of the 

 •"missing links" i^ still to bo seen in the fossil Archaopeteryx. 

 'This extinct creature had a long, tapering, jointed tail, like a 

 lizard ; but each vertebras bore a pair of large quill-feathers 

 spreading horizontally. These feathers on the tail, with those on 

 the wings, were very likely the only ones it possessed. See Fig. 9. 



In the birds of the present day the caudal vertebrfe are few, and 

 very short ; tlie last are joine 1 together into the so-called " plougli- 

 -share bone," which supports the wliole set of quill feathers. The 



