CLAIMS OF OOLOGY TO BE AN EXACT SCIENCE. 239 
differ in shape. But it would be beyond the scope of the 
present paper to go more deeply into this subject, and I 
shall therefore merely point out that in the case of indi- 
vidual aberration the cause is pathological, and that in the 
case of specific aberration it is structural. 
4, SIZE. 
As in the birds themselves, so also in their eggs is there 
great disparity in size. The largest egg of all existing birds 
is that of the Ostrich, and the smallest that of the Humming- 
bird. But while this is commonly the case, it by no means 
follows that the size of the egg is proportionate to the 
dimensions of the bird which lays it. To quote the usual 
stereotyped examples, “the Raven, Curlew, and Guillemot 
are of about equal size, while their eggs vary as ten to one.” 
“The Snipe and the Blackbird,” says Professor Newton, 
“differ but slightly in weight, their eggs remarkably.” The 
egg of the Capercaillie is very small in comparison to the 
size of the bird, that of the Fulmar very large. And in 
individual species, such as the Spotted Flycatcher, the Water 
Rail, and the Sardinian Warbler, not to mention the Cuckoo, 
there is great disparity in the size of the eggs. For com- 
parative purposes, the weight of the bird alone must be taken 
into account; and this renders the task of the oologist the 
more difficult, as the requisite information is, so far as I am 
aware, not obtainable in any English work. Hewitson’s 
solution of the problem is that “the eggs of all birds which 
quit the nest soon after they are hatched, and which are 
consequently more fully developed at their birth, are very 
large.” But the exceptions to this statement are so numer- 
ous, and the division of the Nidifuge from the Nidicole so 
artificial, that it is obvious that other and deeper causes 
must be taken into account. Prof. Arthur-Thomson has an 
ingenious theory, that those birds which are lazy and inordi- 
nately greedy lay proportionally large eggs, while those 
which are very active in their habits lay relatively small 
ones. But this, too, is not borne out by facts. The smallest 
eggs in proportion to the size of the bird are those of the 
