APPENDIX. 367 



■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 j^ossibly have acted ; I 

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

 podidse. The Talcgalla lathami scrapes together a great 

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

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

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

 was estimated at 90° F., 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 Levpoa 

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

 feet in height, of leaves thickly co^xred with sand, and in 

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

 fermentation. The Mcgwpodius tumulus in the northern 

 parts of Australia makes even a much larger mound, but. 

 apparently including less vegetable matter ; and other species 

 in the ]\Ialayan Archipelago are said to j)lace their eggs in 

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

 the sun alone. It is not so surprising that these birds should 

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

 perature is supplied either from fermentation or the sun, as 

 that they should have been led to pile up 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 

 its nest in Mr. Knight's hot-house.t 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- 

 fessor Fischer, " made use of the artificial heat of a hot-bed to 

 hatch her eggs."{ Again Eeaumur, as well as Bonnet, 



* Birds of Australia, and Introduction to the Birds of Australia, 1848 

 p. 82. 



t YarreVs British Birds, vol. i, p. 166. 



X Alison, article "Instinct" in Todd's Cyclop, of Anat. and Physiol., 



