338 LEISURE-TIME STUDIES. 



the bodies of the plant-lice with their antennae, this act causing 

 the plant-lice to exude drops of a clear sweet fluid, of which 

 the ants are extremely enamoured. The ants would thus 

 appear to habitually " milk " their insect-neighbours, and, as 

 far as observation goes, some ants seem not merely to keep 

 the plant-lice in their nests so as to form a veritable dairy- 

 establishment, but also to make provision in the future by 

 securing the eggs of the aphides, and bringing up the young 

 as we rear calves. 



That the relations between the ants and plant-lice are of 

 very stable kind is proved by the interesting remarks of Mr. 

 Darwin, who " removed all the ants from a group of about a 

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

 ance during several hours." Careful watching showed that 

 the plant-lice after this interval did not excrete the sweet 

 fluid. Mr. Darwin then stroked the plant-lice with a hair, 

 endeavouring thus to imitate the action of the ant's feelers, 

 but not a single plant-louse seemed disposed to emit the 

 secretion. Thereafter, a single ant was admitted to their 

 company, the insect, in Mr Darwin's words, appearing, " by 

 its eager way of running about, to be well aware what a rich 

 flock it had discovered." The ant first stroked one aphis, 

 and then another, each insect excreting a drop of the sweet 

 juice " as soon as it felt the antennae ;" and " even the quite 

 young aphides behaved in this manner, showing that the 

 action was instinctive, and not the result of experience." If, 

 as Mr. Darwin remarks, it is a convenience for the aphides 

 to have the sweet secretion removed, and that " they do not 

 excrete solely for the food of the ants," the observation 

 does not in any degree lessen the curious nature of the re- 

 lationship which has become established between the ants 

 and their neighbours, or the interesting features in ant life 

 -.which have inaugurated and perpetuated the habit. 



Not less remarkable are the " slave-making " instincts of 

 certain species of ants. It may be safely maintained that 

 the slave-making habit forms a subject of more than ordinary 

 interest not merely to naturalists but to metaphysicians 



