THE CONDITION OF YOUNG BIRDS AT BIRTH. 115 



contour-feathers of the body and at a much later date than in the 

 above. So also with the nidifugous young of aquatic forms. 



The accelerated development of the quills is probably a remnant 

 of an earlier phase in the life-history before protective coloration was 

 adopted. As we have already shown, precocious flight is attended by 

 too many perils to prove an effective means of escape from enemies. 



In conclusion we may say a word about the young of the megapodes. 

 The eggs of the megapode are, as is well known, hatched in decaying 

 vegetables heaps, or in hot sand, instead of being incubated by the 

 parents. To this end the amount of food-yolk within the egg has been 

 enormously increased, enabling the normal nestling period to be passed 

 within the egg, the young passing through the downy stage during 

 embryonic life, and emerging from the shell, fully fledged. 



That the ancestral megapode was originally hatched in trees like 

 the young hoatzin, there can be no doubt, since like the latter the wing 

 of the young shows a free finger-tip and an arrested development of 

 the outer quill feathers, characters which, as we have already seen, are 

 direct adaptations to the peculiar locomotion of tree-climbing nestlings. 

 We may be almost certain that the increase in the food-yolk, just re- 

 ferred to, did not take place until some time after the descent to the 

 ground for breeding purposes, since the wing of the young megapode 

 forms an exact counterpart of that of the young fowl and turkey, and 

 their allies, whilst, had the increase taken place earlier, the wing 

 would have resembled that of the hoatzin in the possession of large 

 claws. The latter are present now only during embryonic life. 



The increase in the food-yolk, allowing the earlier nestling stages 

 to be passed within the shell, must be accounted for by supposing the 

 adult megapode to have been obliged to adopt this expedient to avoid 

 perils attendant on normal incubation, perils which may since have 

 passed away leaving no record of their nature. A return to the normal 

 method of incubation is now impossible, the instinct therefor having 

 been replaced by that which induces the birds to bury their eggs and 

 leave them to be hatched by heat other than that of their bodies. 



Finally, we may compare the hoatzin with the ancient archasopteryx, 

 and the result of such a comparison will go far to prove that the former 

 represents the most primitive of living birds. 



That archaeopteryx was strictly arboreal there can be no doubt 

 the structure of the feet indicates this much; and its long tail is a 

 scarcely less certain index, for such an appendage is undoubtedly but 

 ill-adapted for ground-dwelling habits. The long hand, and the 

 large claws thereon are, so to speak, primitive characters. The period 

 of their greatest functional activity was during the nestling stage when 

 the young clambered about among the branches of the trees like the 

 young hoatzin of to-day. The species was perhaps not phylogenetically 



