472 LAWS OF MULTIPLICATION. 



one-third. It may be said that the ability of the Partridge 

 to bring up so large a brood, is due to that habit of its tribe 

 which one of its names, " Scrapers," describes ; and to the 

 accompanying habit of the young, which begin to get their 

 own living as soon as they are hatched : so saving the parents' 

 labour. Conversely, it may be said that the inability of 

 Pigeons to rear more than 2 at a time, is caused by the neces- 

 sity of fetching everything they eat. But the alleged relation 

 holds nevertheless. On the one hand, a great part of the food 

 which the Partridge chicks pick up, is food which, in their 

 absence, the mother would have picked up. Though each chick 

 costs her far less than a young Pigeon costs its parents, yet 

 the whole of her chicks cost her a great deal in the shape of 

 abstinence — an abstinence she can bear because she has to fly 

 but little. On the other hand, the Pigeon's habit of laying 

 and hatching but two eggs, must not be referred to any fore- 

 seen necessity of going through so much labour in supporting 

 the young, but to a constitutional tendency established by 

 such labour. This is proved by the curious fact that when 

 domesticated, and saved from such labour by artificial feeding, 

 Pigeons, says Macgillivray (quoting Aitkin), " are frequently 

 seen sitting on eggs long before the former brood is able to 

 leave the nest, so that the parent bird has at the same time 

 young birds and eggs to take care of." 



§ 350. Made to illustrate the effect of activity on fertility, 

 most comparisons among Mammals are objectionable: other 

 circumstances are not equal. A few, however, escape this 

 criticism. 



One is that between the Hare and the Eabbit. These are 

 closely-allied species of the same genus, similar in their diet 

 but unlike in their expenditures for locomotion. The rela- 

 tively-inert Eabbit has 6 young ones in a litter, and four 

 litters a-year; while the relatively-active Hare has but 2 to 

 5 in a litter. This is not all. The Eabbit begins to breed 

 at six months old ; but a year elapses before the Hare begins 



