﻿KIMMERIDGE CLAY. 



89 



In all these gradations of structure in a limb unavailable for flight or any other mode 

 of locomotion we see no approach in the scapula to the Dinosaurian types of that bone ; 

 it retains in all Cursorials the strictly avian sabre-like shape and pointed free extremity, 

 without expansion and truncation there such as obtains in the alleged ancestral Beptilia} 

 The coracoid still further departs from any well-determined Dinosaurian type of the bone, 

 and as closely adheres to that of the Birds of flight, save such decrease of breadth and 

 of relative size as accords with its necessity to bear upon the sternum in the mechanical 

 mode of inspiration peculiar to Birds with Pterodactyles. 



What could be the conceivable conditions of the life of an Iguanodon or Megalosaur 

 which rendered a fore-limb useless or cumbersome, and concomitantly called for lengthened 

 and strengthened hind-limbs and a more vigorous and exclusive exercise of these in the 

 acts of locomotion ? The abettors and acceptors of the exposition of the operation of the 

 secondary mode of origin of species by way of ' natural selection ' are amenable to the call 

 for an explanation of such conditions, especially if such mode of origin be hypothetically 

 applied to the kinds of Birds deprived of the power of flight. But such explanation 

 would have to square with the fact that a loss of one pair of limbs had been associated, 

 on the assumption of the Dinosaurian ancestry, with an advance of the mechanical 

 structure of the organs of circulation, and in the extent and perfection of the lungs, 

 together resulting in the higher temperature, with more numerous and minute coloured 

 discs of the blood. For these conditions of the vital organs characterise alike both winged 

 and wingless Birds, and the resultant unvarying warmth of the body is accompanied by a 

 clothing of down and feathers, the most exquisite and complex of all tegumentary 

 coverings, common to the Kivi and Ostrich with the Eagle and Swift. 



But there are other hypotheses of the way of operation of secondary genesis of species 

 anterior in date to that of Darwin. The influence, viz., of exercise and of disuse in altering 

 the proportions of parts mooted by Lamarck ; 3 the hypothesis of * degeneration ' pro- 

 pounded by Buffbn ; 3 and the effects of congenital changes in parts of the body, 

 mainly depended upon by the author of ' Vestiges,' in his endeavour to explain the way 

 of operation of the secondary law of the origin of species. 



The comparative ease is so refreshing, after the labours of induction and dry descrip- 

 tion, in supposing a case, that I may be forgiven for indulging in a suggestion of a 

 possibility of the few still extant wingless or flightless birds having originated, not from 

 any lower cold-blooded vertebrate form, but from higher active volant members of their own 

 warm-blooded feathered class. Consideration of extinct kinds, in the restoration of which 

 I have been occupied, has strengthened the supposition. 



Here, in yielding to this indulgence, I own to finding more help from the Lamarckian 



1 Compare, for example, the scapula of the Apteryx, 'Transactions of the Zoological Society,' vol. ii, 

 pi. xxx, fig. 2, (j, and figs. 3 and 4, with Cut, fig. 2, p. 31. 



3 ' Philosophic Zoologique,' 2 vols., torn, i, chaps, iii, vi, vii, 8vo, 1803. 

 3 ' Histoire Naturelle,' torn, xiv, p. 311, 4to, 1/66. 



