394 A HISTORY OF BIRDS 



walking and perching. The hind toe or hallux in these birds 

 is long, and in the most strictly arboreal types of great size, 

 while the three remaining toes are large and turned forwards. 



But there are a number of birds which have become adapted 

 to a strictly arboreal life, passing in this environment almost 

 their whole lives, some indeed never leaving the forests, and 

 these have developed feet of a peculiar type, recalling in many 

 ways those of the chameleon. Such are the Parrots, Cuckoos, 

 Kingfishers, Rollers, Bee-eaters, Trogons, Colies and Wood- 

 peckers. In these the feet are used as grasping organs and 

 but rarely for walking. Though the same end has been attained 

 by these very different types of birds, it has been reached by 

 different means, and this is curious. Thus in the Parrots, 

 Cuckoos and Woodpeckers, they are yoked together in pairs, 

 the hallux and outer pointing backwards, the second and middle 

 toes forwards, forming what is known as the zygodactyle foot. 

 The Kingfishers, Bee-eaters and Rollers, for example, have 

 a syndactyle foot, wherein either all the front toes, or the middle 

 and outer toes, are united together throughout the greater part 

 of their length. The foot of the Trogons is unique in that the 

 hallux and second toe turn backwards, instead of the hallux 

 and outer toe, as in Woodpeckers and Cuckoos. In the Swifts, 

 Humming-birds and Colies, or Mouse-birds, the hallux can be 

 turned forwards so that all the toes point forwards. But in all 

 these, save the zygodactyle types, the hallux is relatively small. 

 The Owls have the outer toe reversible at will. Finally, certain 

 Woodpeckers and one Passerine bird have reduced the number 

 of toes to three. 



The wealth of variety in these modifications is curious, inas- 

 much as, so far as we know to the contrary, all are modifications 

 of a common type of foot, adapted to serve the same end. 



Now it is curious to remark that after having undergone 

 a very pronounced adaptation to an arboreal life, certain mem- 

 bers of these groups have exchanged this environment for the 

 ground, and in all these cases the tarso-metatarsus has under- 

 gone a very striking increase in length, as for example, in the 

 Ground Parrakeets of the Genus Pezoporus, the Ground Horn- 

 bill, Ground Cuckoos like Geococcyx, the Dodo, the Solitaire, the 

 Crowned Pigeon and the Tooth-billed Pigeon {Didunculus). On 

 the other hand, by way of baffling speculation, such strictly 



