200 Dr John Davy on the Eggs of Birds. 
fowl, the eggs of other birds have been much neglected,— 
indeed, I am not acquainted with any researches that have 
been published with the intent of ascertaining either the 
proportions of their constituents, or the qualities of these 
constituents, from a comparative point of view. | 
The observations I am about to make, I can offer only as 
a small contribution to so large a subject,—a subject of 
especial interest, considering the vast variety of products,— 
that is, the numerous species of the feathered tribe which 
are evolved, each distinct, yet as soon as hatched, though 
developed from similar elements, displaying the form, tastes, 
and habits characteristic of its kind. I shall first advert to 
some of the general properties of eggs. 
Without exception, the laying birds, whatever their 
species, when in a healthy state and supplied with a suffi- 
ciency of lime, have their eggs enveloped in a resisting shell 
composed of membranes strengthened by an earthy incrusta- 
tion, consisting chiefly of carbonate of lime. The thickness 
of this incrustation in eggs of different birds is very various. 
It seems to bear some relation to the weight of the incubat- 
ing bird, and the time of incubation and hatching. Gene- 
rally, the smaller the bird, and the shorter the period of 
foetal development, the thinner is the incrustation,--the 
elasticity of the shell increasing with its diminution of size. 
I shall give a few instances in illustration, in which, were 
the thickness carefully measured, it would bear, I believe, 
a near proportion to the circumstances mentioned,—of each 
of the following birds, the incubating time is given in 
days :— 
The swan, . . . 42days| The pheasant, . . 28days 
The common goose, 35 ,, The red grouse, . 23 ,, . 
The common duck, 28 ,, Pigeon: t's ae 
The common fowl, 21 ,, Turtle-dovée, © . Vy ia 
The turkey, eh. ee Canary. bird,.. ...kaee 
The guinea-fowl, 30-31 ,, Wren, os os. sls 
The partridge, . . 27 ,, 
These periods are given from such information as I have 
been able to collect from poulterers, bird-fanciers, and 
keepers.* They may not be all quite correct, were they 
* The time of incubation of the following birds, is copied from H. L, Meyer’s 
