NUTRITION AND GENESIS. 479 



tinuous laying, but also in the sizes of the eggs. Among 

 directions given for obtaining eggs from pullets late in the 

 year, it is especially insisted on that they shall have a 

 generous diet. Respecting Pigeons Macgillivray writes: — 

 " that their breeding depends much on their having plenty of 

 food to fatten them, seems, I think, evident from the circum- 

 stance that, when tamed, which they easily are, they are 

 observed to breed in every month of the year. I do not mean 

 that the same pair will breed every month; but some in the 

 flock, if well fed, will breed at any season." There may 



be added a fact of like meaning which partially-domesticated 

 birds yield. The Sparrow is one of the Finch tribe that has 

 taken to the neighbourhood of houses; and by its boldness 

 secures food not available to its congeners. The result is 

 that it has several broods in a season, while its field-haunting 

 kindred have none of them more than two broods, and some 

 have only one. 



Equally clear proof that abundant nutriment raises the 

 rate of multiplication, occurs among Mammals. Compare the 

 litters of the Dog with the litters of the Wolf and the Fox. 

 Whereas those of the one range in number from 6 to 14, those 

 of the others contain respectively 5 or 6 or occasionally 7, and 

 4 or 5 or rarely 6. Again, the Wild Cat has 4 or 5 kittens ; 

 but the tame Cat has 5 or 6 kittens 2 or 3 times a-year. 

 So, too, is it with the Weasel tribe. The Stoat has 5 young 

 ones once a-year. The Ferret has 2 litters yearly, each con- 

 taining from 6 to 9 ; and this notwithstanding that it is the 

 larger of the two. Perhaps the most striking contrast is that 

 between the wild and tame varieties of the Pig. While the 

 one produces, according to its age, from 4 to 8 or 10 young 

 ones once a year, the other produces sometimes as many as 17 

 in a litter; or, in other cases, will bring up 5 litters of 10 each 

 in two years — a rate of reproduction which is unparalleled 

 in animals of as large a size.* And let us not omit to note 

 that this excessive fertility occurs where there is the 



* The climate, the locality, and the kind of food, are of course all factors ; 



