FAMILY CARES — NURSERY DUTIES. 155 



ference is about thiry-six inches, and its capacity 

 about four gallons ! 



The form of the egg varies ; it may be almost 

 perfectly spherical elliptical, oval, or pear-shaped. 



Some owls and the diving - petrel lay round 

 eggs ; in the sand-grouse they are elliptical, oval 

 in the common partridge and turkey, pear-shaped 

 in the plovers. 



The shape of the egg in most birds has ap- 

 parently no definite use or meaning. In the 

 guillemot, however, the long conical form has 

 evidently a definite use. These birds lay their 

 eggs on the bare flat surface of some ledge on a 

 rocky clifi"; when the wind blows with sufficient 

 force to move the egg it turns round upon its 

 small end. If it were round, it would roll off 

 into the sea. In the case of the plover the pear- 

 shape is a most economical one, as, in the nest, but 

 little space is taken up, the eggs being deposited 

 with their small ends inwards, and thus the female 

 is enabled to cover them all when sitting. 



The eggs laid and brooded over at one time, 

 in one nest, form a ^^ clutch." The number of 

 eggs in a clutch varies. The razor-bills of our 

 coasts for instance lay but one, the guillemots 

 two, the sand-grouse three, the common sand- 

 piper four, the robin five, the long-tailed tit nine, 

 the partridge twelve. The number of the eggs 

 in a nest affects their size, for it is necessary that 

 all the eggs in the nest should be covered at the 

 same time by the sitting -bird to ensure their 

 hatching out together. Thus, if the partridge 

 lays twelve eggs, it is obvious they cannot be as 

 large relatively as in the snipe which lays but 



