478 LAWS OF MULTIPLICATION. 



all cases be impolitic; instead of being impolitic only where 

 the growth of sexless axes is still luxuriant. Were it other- 

 wise, a tree which has borne a heavy crop should, by the 

 consequent 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 yielded by animals — those 

 animals at least in which we have, besides an increased sup- 

 ply 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 comparisons 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 

 13 to 18 eggs and often sits a second time; 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 livia 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 inequalities of fertility are 

 caused by inequalities in the supplies of food, is a familiar 

 truth. High feeding shows its effects not only in the con- 





