NUTRITION AND GENESIS. 457 



a tree which has borne a heavy crop, should, by the con- 

 sequent depletion, be led to bear a still heavier crop next 

 year ; whereas it is apt to be wholly or partially barren next 

 year — has to recover a state of tolerably-high nutrition 

 before its sexual genesis again becomes large. 



But the best illustrations are those yielded by animals, 

 in which we have, besides an increased supply of nutriment, 

 a diminished expenditure. Two classes of comparisons, alike 

 in their implications, may be made — comparisons between 

 tame and wild animals of the same species or genus, and com- 

 parisons between tame animals of the same species differently 

 treated. 



To begin with Birds, let us first contrast the farm-yard 

 Gallinacece with their kindred of the fields and woods. Not- 

 withstanding their greater size, which, other things equal, 

 should be accompanied by smaller fertility, the domesticated 

 kinds have more numerous offspring than the wild kinds. A 

 Turkey has a dozen in a brood, while a Pheasant has from 6 

 to 10. Twice or thrice in a season, a Hen rears as many 

 chickens as a Partridge rears once in a season. Anserine birds 

 show us parallel differences. The Tame Goose sits on 12 or 

 more eggs, but the Wild Goose sits on 5, 6, or 7 ; and these 

 are noted as considerably smaller. It is the same with Ducks : 

 the domesticated variety lays and hatches twice as many eggs 

 as the wild variety. And the like holds of Pigeons. After 

 remarking of the Columba licia that "in spring when they 

 have plenty of corn to pick from the newly-sown fields, they 

 begin to get fat and pair ; and again, in harvest, when the 

 corn is cut down, " Macgillivray goes on to say, that " the 

 same pair when tamed generally breed four times" in the 

 year. That between different poultry-yards, in- 



equalities of fertility are caused by inequalities in the supplies 

 of food, is a familiar truth. High feeding shows its effects not 

 only in the continuous laying, but also in the sizes of the 

 eggs. Among directions given for obtaining eggs from 

 pallets late in the year, it is especialty insisted on that tbey 



