4:34 LAWS OF MULTIPLICATION, 



by the Cod, the fertility of the species may De greater not* 

 withstanding the smaller number produced b}' each indi* 

 vidual. Evidence that admits of being tolerably 



well disentangled is furnished by Birds. They differ but 

 little in their grades of organization ; and the habits of life 

 throughout extensive groups of them are so similar, that 

 comparisons may be fairly made. It is true that, as hereafter 

 to be shown, the differences of expenditure which differences 

 of bulk entail, have doubtless much to do with the differences 

 of fertility. But we may set down under the present head 

 some of those cases in which the activity, being relatively 

 slight, does not greatly interfere with the relation we are 

 considering ; and may note that among such birds having 

 similarly slight activities, the small produce more eggs than 

 the large, and eggs that bear in their total mass a greater 

 ratio to the mass of the parent. Consider, for example, the 

 gallinaceous birds ; which are like one another and unlike 

 birds of most other groups in flying comparatively little. 

 Taking first the wild members of this order, which rarely breed 

 more than once in a season, we find that the Pheasant has 

 from 6 to 10 eggs, the Black-cock from 5 to 10, the Grouse 

 8 to 12, the Partridge 10 to 15, the Quail still more, some- 

 times reaching 20. Here the only exception to the relation 

 between decreasing bulk and increasing number of eggs, 

 occurs in the cases of the Pheasant and the Black-cock ; and 

 it is to be remembered, in explanation, that the Pheasant 

 inhabits a warmer region and is better fed — often artificially. 

 If we pass to domesticated genera of the same order, we 

 meet with parallel differences. From the numbers of eggs 

 laid, little can be inferred ; for under the favourable con- 

 ditions artificially maintained, the laying is carried on inde- 

 finitely. But though in the sizes of their broods the Turkej^ 

 and the Fowl do not greatly differ, the Fowl begins breeding 

 at a much earlier age than the Turkey, and produces 

 broods more frequently : a considerably higher rate of 

 multiplication being the result. JSTow these contrasts 



