AITENDIX. 307 



under its own conditions of life ; and if the nesting-instinct 

 varies ever so little, when a bird is placed under new con- 

 ditions, and the variations can be inherited, of which there 

 can be little doubt — then natural selection in the course of 

 ages might modify and perfect almost to any degree the nest 

 of a bird in comparison with that of its progenitors in long 

 past ages. Let me take one of the most extraordinary cases 

 on record, and see how selection may possibly have acted; I 

 refer to Mr. Gould's observation* on the Australian Mega- 

 podidse. The Talegalla lathami scrapes together a great 

 pyramid, from two to four cart-loads in amount, of decaying 

 vegetable matter; and in the middle it deposit its eggs. The 

 eggs are hatched by the fermenting mass, the heat of which 

 was estimated at 90° R, and the young birds scratch their 

 way out of the mound. The accumulation propensity is so 

 strong that a single unmated cock confined in Sydney annually 

 collected an immense mass of vegetable matter. The Leipoa 

 oeellata makes a pile forty-five feet in circumference and four 

 feet in height, of leaves thickly covered with sand, and in 

 the same way leaves its eggs to be hatched by the heat of 

 fermentation. The Megapodiua tumulus in the northern 

 parts of Australia makes even a much larger mound, but 

 apparently including less vegetable matter; and other species 

 in the Malayan Archipelago are, said to place their eggs in 

 holes in the ground, where they are hatched by the heat of 

 the sun alona It is not so surprising that these birds should 

 have lost the instinct of incubation, when the proper tem- 



ture is supplied either from fermentation or the sun, as 

 thai they should have been Led to pile np beforehand a great 

 heap of vegetable matter in order that it might ferment ; 

 for, however the fact may be explained, it is known that 

 other birds will leave their eggs when the heat is sufficient 

 for incubation, as in the case of the Fly-catcher which built 



nesl in Mr. Knight's hot-housat Even the snake takes 

 advantage of a hot-bed in which to lay its eggs; and what. 

 concerns us more, is that a common hen, according to Pro- 



or Fischer, " made ose ol the artificial heat of a hot-bed to 

 hatch her eggs."f Again Reaumur, as well as Bonnet, 



• It i nli of Australia, ;ni'l 1 ut rwl 1/1 I mn U) tko Units of Australia, IMS, 



f ]arrrt'M It ninth ltir,U \,,\ i j, lilt". 



* Alkoo, urlulo " ImliiRt " in TwIli Cyclop, of Anit. ami PkwtioL, 

 p. th 



