90 The Rev. P. Keith o?i the Structure of Animals, 



By adhering to the method by combinations or symmetrical 

 functions, the complete formula 



(.r^ — SI -f-j9) {(3« — s) x'^ — ^{as — 'p)x-\-a'p} = 0, 



would have resulted in place of (C), which contains only the 

 latter factor; and the evidence adduced would have been 

 somewhat more clear. 



XIV. Of the Sti-ucture of Animals. 5j/ Me .R^t;. Patrick Keith, 

 F.L.S.y &c. 

 [Concluded from p. 16.] 



Class2, TF we look at an individual of the class of Birds, we 

 -*- shall find that it exhibits the same general type of 

 structure with that of the Mammalia, consisting ofhead, neck, 

 body, limbs. The head, as in the foregoing class, is the seat of 

 the organs of sense, furnished with and terminating in a bill, by 

 which the individual picks up and breaks its food. The form 

 of the bill differs much in different species, and serves as a 

 mark to discriminate tribes or families. The head, neck, and 

 body are covered with feathers, which are often adorned with 

 the brightest and most brilliant colours. The neck assumes 

 the circular form, and often displays peculiar beauty, as well 

 as peculiar flexibility, as any one who has seen a swan in the 

 act of swimming will, with Milton, readily admit : 



" The swan, with arched neck 



Between her white wings mantling, proudly rows 

 Her state with oary feet." — Paradise Lost, b. vii. 



The greatest bulk of the body is around the breast, tapering 

 towards the tail, which is composed of feathers of a peculiar 

 form, — magnificently illustrated in the tail of the peacock. The 

 fore limbs assume the position and fan-like form of wings, to 

 fit the individual for its flight in air; and are often composed 

 of, or rather covered with, a plumage that is most splendidly 

 brilliant. The hinder limbs always terminate in feet, divided 

 into toes tipped with claws, some genera having the toes sepa- 

 rate, as the pheasant and partridge ; and some having them 

 united with a membrane, as the swan and goose. The former 

 are land birds ; the latter are water, or web-footed birds. 



Class 3. In this class, the class of Fishes, the vestiges of 

 the general type, though much metamorphosed, can still be 

 readily traced. The head is very distinctly visible, furnished 

 with its projecting mouth and devouring jaws. The eyes are 

 sufficiently conspicuous ; but the other organs of sense have 

 no very visible development of external parts. The head is 



