130 THE INFANCY OF ANIMALS 



of the food-yolk did not take place until some time after 

 the descent from the ground for nesting purposes, since 

 the wing of the nestling megapode forms an exact counter- 

 part of that of the young fowl or turkey. Had the increase 

 taken place earlier, the wing would more closely have 

 resembled that of the young hoatzin in the possession 

 of large claws. These are now present only during em- 

 bryonic life. 



This increase in the amount of the food-yolk, allowing 

 the earlier nestling stages to be passed within the egg, 

 must be accounted for by supposing the adult megapode 

 to have been obliged to adopt this expedient to avoid the 

 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 im- 

 possible, the instinct therefor having been replaced by that 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 the brooding bird. 



The interpretation of the facts herein recorded is surely 

 well supported by evidence. Yet a diametrically opposite 

 rendering has been formulated, which certainly will not 

 bear criticism. The great size of the egg, it has been held, 

 takes up so much room within the body cavity, that only 

 one can ripen at a time, and consequently long intervals 

 must elapse between the deposition of each egg. To wait 

 till aU were laid before commencing incubation, they say, 

 would be dangerous, and furthermore, they could not all 

 be covered by the sitting bird. Consequently, each is 

 deposited as it is laid, in an incubator, and left to take its 

 chance, just as among the reptiles. 



It is held, in short, that the megapodes lay their eggs 

 in mounds because of their size. The converse is certainly 

 the case — the large egg has been produced because of the 



