230 INSTINCT. 



I watched them for some time through a lens, but not on* 

 excreted ; I then tickled and stroked them with a hair in 

 the same manner, as well as I could, as the ants do with 

 their atennse; but not one excreted. Afterward, I allowed 

 an ant to visit them, and it immediately seemed, by its eager 

 way of running about to be well aware what a rich flock it 

 had discovered ; it then begun to play with its antennae on 

 the abdomen first of one aphis and then of another ; and 

 each, as soon as it felt the antennae, immediately lifted up 

 its abdomen and excreted a limpid drop of sweet juice, which 

 was eagerly devoured by the ant. Even the quite young 

 aphides behaved in this manner, showing that the action was 

 instinctive, and not the result of experience. It is certain, 

 from the observations of Huber, that the aphides show no 

 dislike to the ants : if the latter be not present they are at 

 last compelled to eject their excretion. But as the excretion 

 is extremely viscid, it is no doubt a convenience to the 

 aphides to have it removed ; therefore probably they do not 

 excrete solely for the good of the ants. Although there is 

 no evidence that any animal performs an action for the 

 exclusive good of another species, yet each tries to take 

 advantage of the instincts of others as each takes advan- 

 tage of the weaker bodily structure of other species. So 

 again certain instincts cannot be considered as absolutely 

 perfect ; but as details on this and other such points are 

 not indispensable, they may be here passed over. 



As some degree of variation in instincts under a state of 

 nature, and the inheritance of such variations, are indis- 

 pensable for the action of natural selection, as many instances 

 as possible ought to be given ; but want of space prevents 

 me. I can only assert that instincts certainly do vary — for 

 instance, the migratory instinct, both in extent and direc- 

 tion, and in its total loss. So it is with the nests of birds, 

 which vary partly in independence on the situations chosen, 

 and on the nature and temperature of the country inhabited, 

 but often from causes wholly unknown to us. Audubon has 

 given several remarkable cases of differences in the nests of 

 the same species in the northern and southern United States. 

 Why, it has been asked, if instinct be variable, has it not 

 granted to the bee " the ability to use some other material 

 when wax was deficient ? " But what other natural material 

 could bees use ? They will work, as I have seen, with wax 

 hardened with vermilion or softened with lard. Andrew 

 Knight observed that his bees, instead of laboriously collect- 



