INCUBATION. 267 



quarters from the foot to the knee. In all the above varieties of this 

 species, the conformation of the bill and legs, in shape and length, is a 

 strong proof that they are the same : another strong characteristic dis- 

 tinction, is the back toe, which is long, and a continuation of the heel, 

 or plant of the foot. 



The Ibis is adopted as a part of the arms of the town of Liverpool, 

 and formerly, if not at present, stood conspicuous upon the Guildhall 

 in truly golden array. This is termed a liver, from which that flou- 

 rishing town derived its name, and is now standing on the spot where 

 the pool was, on the verge of which the liver was killed. * 



ICE-BIRD. — A name for the Rotche or little Auk ( Uria Alle, 

 Temminck.) 



ICELAND GULL. — * Temminck and Captain Sabine give this as 

 a variety of the Silvery Gull (Larus argentatus) ; Dr. Fleming makes it 

 a distinct species (L. Islandicus.) 



IMBER DIVER.— A name for the Loon. 



INCUBATION. — It is probable birds are endowed with an in- 

 stinctive power of regulating the necessary heat for this purpose ; of 

 course, should the heat of the air, together with the natural warmth of 

 the body, on the close contact of the bird to the eggs, be too great, her 

 feelings would dictate the necessity of leaving them for a time to cool. 

 At the early period of incubation birds quit their eggs more frequently 

 than at the time the foetus is more perfect. Yet, in the advanced state, 

 the embryo young is not in more danger of being destroyed, if so 

 much ; for we have frequently found a living foetus in an egg that has 

 been taken from the nest two days. If, however, the young is within 

 a few hours of being excluded, and the egg is suffered to be some time 

 cold, it either dies, or becomes so weak, as not to be able to extricate 

 itself from the shell. Various degrees of heat will enlarge the embryo 

 young, but regular heat seems necessary to its production ; and yet 

 artificial heat, regulated by the brooding of a bird, will not produce 

 young with such certainty. In Egypt, a vast quantity of eggs are 

 hatched by artificial heat in stoves. It is probable, however, one third 

 or one fourth miscarry. The necessary heat for this purpose is about 

 ninety-six degrees of Fahrenheit's thermometer, or thirty-two of Reau- 

 mur's scale. Birds frequently turn and change the situation of their 

 eggs in the nest ; besides this, it is possible the moisture of the bird's 

 body may assist the natural growth of the foetus and production of the 

 young. 



The male birds of some species supply the place of the female on the 

 nest ; but then it is of short duration, and rarely, if ever, when the eggs 



