Chap. TOL] INSTINCT. 323 



ing an action for the sole good of another, with which I 

 am acquainted, is that of aphides voluntarily yielding, 

 as was first observed by Huber, their sweet excretion to 

 ants : that they do so voluntarily, the following facts 

 show. I removed all the ants from a group of about 

 a dozen aphides on a dock-plant, and prevented their 

 attendance during several hours. After this interval, I 

 felt sure that the aphides would want to excrete. I 

 watched them for some time through a lens, but not one 

 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 antennas ; but not one excreted. Afterwards 

 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 began 

 to play with its antennas on the abdomen first of one 

 aphis and then of another ; and each, as soon as it felt 

 the antennas, 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 ; there- 

 fore 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 advantage of the weaker bodily 

 structure of other species. So again certain instincts 



