ANIMAL ARITHMETIC. 255 



their nests, for we can not take one out without causing in them 

 a disquiet that becomes greater if we remove more. But they 

 manifest a like distress when their eggs are only disarranged. Is 

 this because the geometrical arrangement of the eggs is changed ? 

 Five eggs or four make a symmetrical arrangement as the bird 

 disposes of them. But if some are taken out, and three, or two, 

 or one are left, the disposition is very perceptibly changed. 

 When the little birds have been hatched, the differences in their 

 size, liveliness, figure, and voice, give the mother a means of dis- 

 tinguishing them individually. And even the eggs are perhaps 

 not so indistinguishable to her as to us ; for sexual and maternal 

 instinct conveys special faculties in these matters. The domestic 

 fowl seems to be less intelligent in such things than sparrows and 

 other wild birds, but this is because domestication has modified 

 her instincts. 



Cats certainly know how many kittens they have, but they 

 seem less affected by the loss of one of them according as more 

 are left. If the mother loses one of four or five, she seeks for it 

 a little while with considerable anxiety, and then becomes recon- 

 ciled to the loss. If only one is left, she becomes greatly troubled, 

 and, if that is taken from her, her distress appears extreme. This 

 may be because of the pain she suffers in her teats when the milk 

 ceases to be removed. When the young have become weaned, she 

 can witness their disappearance with apparent indifference. 



Dogs have been observed on various occasions to exhibit pri- 

 mary numerical perceptions in the concrete. When there are a 

 number of them in a house, they quickly remark the absence of 

 one of their companions. But they are rarely troubled by it, and 

 make no effort to find the missing one, and they are still more 

 ready to take notice of the absence of one of the members of their 

 master's family. These traits are more easily explained by the 

 clear knowledge which dogs have of individualities than by 

 ascribing to them notions of unities as forming parts of numbers. 

 The unequal degrees of attachment which they show for the dif- 

 ferent members of the family, and for the different persons who 

 live in the house or visit it, proves that they make great differ- 

 ences between them. The idea of difference between several per- 

 sons involves and supports a notion of their number. But it may 

 lie there if wrapped up in their total perception. 



Hounds pursuing a hare are troubled for an instant if they 

 raise another one, and will sometimes stop, as if they were uncer- 

 tain which one they ought to follow. Good dogs will not allow 

 themselves to be diverted from the scent of the first animal, which 

 they have already tired. When the setter pauses before a flock 

 of partridges, the movements of his head and eyes follow the birds 

 that stray to the right or left. If the flock is large, he can not 



