As a further illustration, let us take the eggs of the Golden and Green Plovers, and consider for a moment their size, shape, number, and colour. All these qualities serve some well-defined and demonstrably useful end. Firstly, their size is abnormally large compared with that of the layer, but this is a provision which supplies the necessary size and strength of the young bird to enable it to cope with the surrounding conditions of its first days of self-feeding and locomotion amongst coarse grass and other obstacles. Secondly, the shape of the egg serves to economise space, an important point where the eggs are large and the bird small. Thus the four pear-shaped eggs, having their small ends all pointing to a common centre, practically form a square, and thus enable the bird to cover them all at the same time. Thirdly, the number of eggs is always four, and by such limitation the form of the square is preserved, and the difficulty of a small bird covering a number of large eggs satisfactorily surmounted. I have often disarranged the order of Plovers' eggs, but always found that the first thing done by the bird on her return was to reduce chaos to order by turning the round ends out and the small ones into the centre of her little household. Lastly, we come to the beautiful harmony of colouring of the eggs with surrounding objects, rendering them often very difficult to find, even by a practised eye, and the scant nest still further aiding in the chances against discovery. The Sandpiper affords an admirable instance of the assimilation of its eggs to surrounding objects, and the extreme difficulty experienced in finding them attests to its protective utility. =Why Eggs Vary so much in Point of Number.=--The number of eggs laid by birds of different orders seems to be regulated by the danger to which they are exposed and the amount of food which the parents will be able to supply. Thus, the Eagle in its inaccessible eyrie enjoys almost perfect immunity from danger, and has only two young ones, for which, however, the supply of food is only equal to the demand, and it is probable that one more voracious appetite would seriously endanger the safety of the whole family. On the other hand, take the Common Partridge with its sixteen or twenty eggs, the high percentage of its dangers, and the generally abundant supply of food.