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 

 GallinacecB 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 theae 

 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 Cohnnba 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 

 e^gs. Among directions given for obtaining eggs from 

 pullets late in the year, it is especially insisted on that they 



