Vol. xxxvi.] 16 



spheroidal or ovoid shape by the exigences of its position in 

 the oviduct and the necessity of passing along it, there are 

 few facts in nature more remarkable^ I niay say astounding, 

 than the infinite variety in shape, size, colour, texture^ and 

 markings. Is this all meaningless ? To take the question 

 of shape first ; it is clear that it must be regulated by pres- 

 sure of the upper part of the oviduct walls acting on the 

 resistance of the egg itself while the calcareous covering is 

 still soft. M. Hardy first suggested that the normal position 

 of the parent would affect the shape of the egg. For 

 example, the Caprimulgus spends most of its time in a prone 

 attitude, and so lays a cylindrical egg, because it lies in the 

 oviduct horizontally ; while a Kingfisher or Bee-eater, 

 adopting an upright position, lays a spherical egg, because 

 the downward pressure and weight of the egg operate 

 against the long axis. This theory, propounded in 1857, 

 was rediscovered in 1891 by Dr. Nicolskj'-, and introduced 

 as a novelty to the notice of the B. O. U. in the 'Ibis ' for 

 1893. Pyriform eggs are supposed to be laid by birds 

 which adopt both positions, such as Guillemots. Seebohm, 

 in the paper referred to, suggested that long-legged birds 

 hatched in an advanced stage of development, required 

 elongated or pyriform eggs, while short-legged " prsecoces " 

 and even long-legged '' altrices " laid rounder eggs. There 

 is probably more than a fraction of truth in both theories, 

 which connect the structure of the bird and that of the Q^%, 

 but neither will explain every case. Then, when we come 

 to consider size, we find that the e^^ is by no means always 

 proportioned to that of the parent. The Cuckoo lays an 

 egg sometimes smaller than a Sparrow's; the Apteryx lays 

 a huge egg, which is a quarter of its own weight. Roughly 

 speaking, size depends on the stage of development in the 

 chick when hatched. In some groups, where the eggs are 

 laid on the ground, the chicks are necessarily much more 

 advanced than when they have the protection of a nest, 

 where they ai-e out of the way of many dangers. The length 

 of the incubation period must also be taken into considera- 

 tion, so that here we see a direct connection between the 

 habits of a bird and the size of its egg. 



