EGG 



1961 



EGG 



the all-important vesicle, or germ, from which 

 the young bird is developed by incubation. 



Hatching. The embryo can be developed 

 only in one way, and that is by the applica- 

 tion of heat. Occasionally, in the case of 

 domestic fowls, this heat is artificially fur- 

 nished, by some sort of an incubator (which 

 see) ; but in nature the heat is supplied by 

 the body of the female as it sits on the nest. 

 In some species of birds the male sits on the 

 eggs during the hatching period. A tempera- 

 ture of about 104 is needed to develop the 

 eggs of fowls and most other birds, but there 

 is a difference in the time required for hatch- 

 ing. Some small birds brood their eggs only 

 about a week, but it takes three weeks to 

 hatch the eggs of the hen, while those of the 

 goose and turkey need four weeks of incuba- 

 tion. 



Number and Size of Birds' Eggs. A full 

 "set" or "clutch" consists of from one to 

 twenty eggs, the number in a set being about 

 the same for each species of birds. Among 

 different species, however, the number varies 

 greatly. The largest families are found among 

 those whose young come into the world with 

 a covering of down, and are able to run about 

 as soon as they are hatched. Such birds re- 

 quire comparatively little care, and a numer- 

 ous brood does not overtax the parents. The 

 largest numbers are laid by members of the 

 grouse, quail and duck families, represented 

 by the teal, whose set comprises fifteen eggs; 

 and by the partridge, which lays from twelve 

 to twenty. The size of the parent bird, how- 

 ever, is also a determining factor, small birds 

 never laying more eggs than their bodies will 

 cover. But four young, for example, are 

 hatched by the snipe and plover, though their 

 little ones are not wholly dependent on the 



older birds. The number of eggs laid in a 

 season is sometimes affected by accidental 

 causes. For instance, when a nest is robbed 

 the birds will often replace the stolen eggs. 

 There is on record the case of a flicker, which 

 laid seventy-one eggs in seventy-three days. 



Generally speaking, the size of an egg is 

 governed by the size of the bird which lays it ; 

 the ostrich, largest of all birds, lays an egg 

 about six inches long, weighing nearly three 



rotem,l48 

 at. 105 



COMPOSITION OF A HEN'S EGG 



The above percentages include the contents 

 of the entire egg. The illustration next follow- 

 ing gives the analysis of white and yolk sep- 

 arately. 



pounds. From this size eggs of birds range 

 down to the egg of the tiny humming bird. 

 However, eggs of birds whose young are able 

 to care for themselves are relatively larger 

 than those of birds whose offspring emerge 

 from the shell in a helpless, immature con- 

 dition, for the former must remain in the 

 protective shell a longer time than the less 

 developed birds, and they must have suffi- 

 cient room in which to grow. For this reason 

 the spotted sandpiper, though about the size 

 of the robin, lays an egg considerably larger 

 than the robin's; likewise the meadow lark luys 

 a much smaller egg than the upland plover, 

 though the birds are practically equal in sixe. 



Eggs as Food 



All over the world people use eggs as food, 

 the eggs of fishes and reptiles furnishing not 

 only delicacies but staples in some localities; 

 but it is theeggs of birds, and especially of 

 the domestic fowl, to which most importance 

 attaches. 



Food Value. An egg is almost as perfect a 

 food as milk, but it lacks one valuable element 

 which milk possesses, for it hus practically no 

 carbohydrates (which see). If served with 

 something which supplies this lack, however, 

 as 'rice, white bread or potatoes, eggs consti- 

 tute an ideal food. They are easily and 



thoroughly digested, too, by nearly everybody. 

 As regards its constituent parts, an ogg, 

 freed from its shell, consists of 73.7 per cent 

 water, 145 per cent protein, 10.5 per cent fat 

 and about one per cent ash, and has a fuel 

 value per pound of 720 calories (see CAUWIK; 

 FOOD, subhead Chemistry oj Food). Com- 

 paratively spouking, tho yolk has fur more of 

 the nutrient elements than has tho white, the 

 latter being 86.2 per cent water, 13 IKT cent 

 protein, 0.2 per cent fut and 0.6 per cent :uh, 

 and having a fuel value of 250 calorics to the 

 pound, while the yolk is 49.5 per cent water, 



