Vol. VIII 

 1909 J 



] Mattingley, Thermometer-Bird or Mallee-Fowl. II7 



interference. Sometimes, however, only three eggs constitute - 

 the lower tier, which is the first of the series deposited in the 

 egg-chamber. There is no regular spacing between the eggs 

 forming any one tier, but the eggs comprising it are usually on 

 the same plane, being uniformly level ; yet this formation is 

 not constant. The eggs are separated from one another by 6 to 

 12 inches of sand, and are placed close to the solid, interlaced 

 decaying vegetable matter forming the wall of the egg-chamber. 

 This position serves two purposes — firstly, it brings the eggs 

 near to the warmth radiated by the decomposing vegetable 

 mass, and, secondly, it also prevents undue lateral pressure that 

 would otherwise fall on the weakest part — i.e., the side of the 

 sg?» ss it reposes vertically in the mound, and thus prevents the 

 egg from being crushed by the superimposed mass of sand or 

 gravel, which is usually heaped about 2 feet high above them, 

 as well as being banked several feet thick through the walls 

 that compress the material of the egg-chamber on all its sides. 

 It was probably due to these causes that the egg-chamber itself 

 was evolved. This hypothesis is all the more feasible on 

 account of the circular design of the architecture of the inner 

 walls of the chamber. Were the birds to build a square egg- 

 chamber, that mode of structure would more readily collapse 

 should the mound become displaced by a cyclone or by other 

 means. Being composed externally of loose sand or gravel, 

 which material is apt to shift bodily, owing to its instability, 

 too great a pressure would be exerted on the external 

 parts of the egg-chamber, which, if square, would more easily 

 collapse, and render the eggs liable to destruction. The circular 

 method, also, of the structure of the shaft or funnel which forms 

 the receptacle for the eggs, is much less liable to damage, since 

 the pressure is exerted evenly over its surface, whilst it would 

 spin around with the mound should it be moved by any cause, 

 such as by whirlwinds, which are of common occurrence in the 

 hot, sandy districts of Australia. Above the first, or bottom tier 

 three or four more tiers or circles of eggs, one tier above the 

 other, are deposited, with no one &gg immediately over another. 

 Sometimes the eggs in the tiers will number — 



Tier. No. i Mound. No. 2 Mound. No. 3 Mound. No. 4 Mound. 



I St (bottom) 4 eggs 4 eggs 3 eggs 5 eggs 



2nd ... 5 „ 6 „ 5 )' 6 „ 



3rd ... 3 )) 4 )) 4 J) 4 )> 



4th , ... 3 » 2 „ 



Usually 3 or 4 inches of sand divide the eggs in one tier from 

 those in another, but this is not constant. The temperature 

 of the egg-chamber varies from 90 degrees to 97 degrees, which 

 heat is sufficient to hatch out the eggs successfully. The bird, 

 however, as before stated, regulates the temperature according to 



