92 ZOOLOGICAL GARDENS. 



ture common to all the species may perhaps be reduced 

 to two ; the strong curvature of their rounded bills, and 

 the uniformly zygodactyle character of their toes, the 

 two middle ones being alone directed forwards, and 

 their action being counterbalanced by the outer and the 

 inner, which are constantly retroverted. To these 

 characters may be added, as more or less generally 

 applicable, the presence of a membranous cere envelop- 

 ing the base of their mandibles, but sometimes scarcely 

 visible upon the upper; the large size and fleshy con- 

 sistence of their tongue ; the strength and curvature of 

 their claws ; the general brevity of their legs, which 

 are mostly covered in front with large reticulated scales ; 

 and the comparative shortness of their wings. 



But even in the more essential of these characteristics 

 the modifications are both numerous and striking. The 

 bill for instance is subject to considerable variation ni 

 its comparative size, its proportional length, the degree 

 of its curvature, and the form of its cutting edges. The 

 tongue, which in most of the subdivisions is thick, 

 fleshy, and of uniform structure throughout, in others 

 terminates in a brush-like bundle of filaments, and in a 

 third modification consists merely of a hollow gland, of 

 a somewhat horny consistence, supported by a cylin- 

 drical exsertile and retractile pedicel. The tarsi too, 

 which are in general short and thick, are in some 

 instances so much elongated as to enable the birds in 

 which this structure obtains to run upon the ground 

 with a facility approaching to that of the Gallinaceous 

 tribes. All these modifications are so evidently con- 

 nected with essential differences in natural habits, as 

 to point out at once the necessity of subdivision in this 

 extensive family. In this subdivision material assistance 

 is derived from the tail, which passes through every 

 intermediate gradation between the short rounded form 



