172 THE BIOLOGY OF THE SEASONS 



creatures, and this limits the number of relatively large 

 eggs that they can bear at a time. On the other hand, 

 the great care that birds take of their eggs and young 

 makes survival, in spite of the small family, more practicable. 

 And, again, it must be remembered that many birds are 

 taxed to the utmost in feeding their young brood, so that 

 in this way an indirect check would be put on large 

 clutches. 



The size of the egg depends, as in most cases, on the 

 amount of nutritive material or yolk, not on the amount 

 of living matter that there is to start with. In general 

 it bears some relation to the size of the bird. Of European 

 birds, the swans have the largest eggs, and the golden- 

 crested wren the smallest. It is said that the egg of the 

 extinct Moa of New Zealand sometimes measured 9 in. 

 in breadth and 12 in. in length, while that of the extinct 

 ^pyornis of Madagascar held over two gallons some six 

 times as much as an ostrich's egg, or a hundred and fifty 

 times as much as a fowl's. 



It cannot be said, however, that the size of the egg is 

 more than generally proportional to that of the parent ; 

 for, while the cuckoo is much larger than a lark, the eggs 

 of the two birds are about the same size ; and, while the 

 guillemot and the raven are about the same size, the eggs 

 the former are in volume about ten times larger than of 

 those of the latter. Hewitson pointed out that " the eggs 

 of all those birds which quit the nest soon after they are 

 hatched, and which are consequently more fully developed 

 at their birth, are very large." Professor Alfred Newton 

 adds that " the number of eggs to be covered at one time 

 seems also to have some relation to their size." He con- 

 trasts the snipe and the partridge : the former has four 

 eggs, the latter as many as twelve ; the eggs are equal in 

 size, and the chicks in both cases are able to run about as 



