BIRDS' EGGS 273 



they are hatched. Mr. Edward J. Bedford gives the follow- 

 ing illustrations : " The Common Snipe and the Blackbird 

 are about the same size, and while the average size of the egg 

 of the former is i'58 inches by i"i inches, that of the latter 

 is only i*i8 inches by 0-85 of an inch. The Curlew, Raven, 

 and Guillemot are all about the same size, and while the 

 average measurements of the egg of the Raven are i'95 inches 

 by 1*3 inches, that of the Curlew is 2*65 inches by i"85 inches, 

 and the Guillemot 3*25 inches by 1*95 inches." 



Shape, — Most eggs are obviously oval, and this shape is 

 related to the conditions of muscular pressure within the 

 oviduct before the shell consolidates. In owls and some 

 other birds the eggs are approximately spheres, and this is a 

 retention of the shape of the ovarian egg. Those of the 

 sand-grouse are almost cylindrical with obtuse ends ; those 

 of grebes are wide in the middle and equally pointed at the 

 two ends so that they approach a biconical shape. In fowls 

 and the like there is great variety in the precise shape, and 

 strange abnormal freaks are not uncommon. In a large 

 collection of eggs with many examples of the same species 

 the variability of shape within narrow limits is very evident, 

 and we understand again that in the course of time there 

 may have come about by selection a fixing of the fittest 

 shape. This is not inconsistent with the determination of 

 the shape by the conditions of pressure in the oviduct, for 

 these depend on the structure and constitution of the hen- 

 bird — likewise subject to variation. 



It is probable that the shape of the enshelled egg is most 

 important in relation to the process of being passed down the 

 lower part of the oviduct and laid. The broad end is always 

 first. But there are cases where another utility may be 

 recognised. Thus in the eggs of most Limicolae (snipe, 

 plover, and their relatives) there are four eggs which lie with 

 their narrow ends almost touching in the centre, so that there 

 is economy in the space to be covered by the brooding bird. 



Darwin pointed out that the single egg of a guillemot or 

 a razorbill is laid on the narrow shelf of a precipitous sea- 

 chff . It is hable to be jostled by the wind or by the parents' 



T 



