290 THE STORY OF THE BIRDS 



counteracts the pressure of the ovary ; whilst 

 birds which lay oval eggs maintain a horizontal 

 attitude, the weight of the egg then assisting the 

 pressure of the ovary ; and lastly, birds which 

 lay pyriform eggs frequently change their posi- 

 tion from a vertical one when standing to a hori- 

 zontal one when flying or swimming. Seebohm, 

 on the other hand, has suggested a possible cor- 

 relation between the state in which the young 

 are hatched with the shape of the egg, the long- 

 legged praecoces laying pyriform eggs and the 

 short-legged altrices laying round eggs, whilst 

 the long-legged altrices and the short-legged 

 praecoces produce oval eggs. The subject re- 

 quires much more elaborate investigation than it 

 has hitherto received before any conclusion can 

 be drawn. 



Now a few words concerning the size of eggs. 

 Here again we do not mean the variation in this 

 respect amongst the eggs of a single species or 

 individual (although this is much greater than is 

 generally suspected), but more the proportion- 

 ate size in relation to the parent in the several 

 orders and families. A big bird by no means 

 always lays a big egg, neither does a small bird 

 always lay a small one. In some species this dis- 

 proportion between the egg and its parent is very 



