66 ANIMAL INTELLIGENCE. 



likewise. Then some of the masters came out, and, by 

 pulling the legs of the feeding slaves, reminded them that 

 they were neglecting their duty. The slaves then imme- 

 diately began to serve their masters with the sugar. Forel 

 also has continued all these observations of Huber. Indeed, 

 in the case of F. rufescens, the structure of the animal is 

 such as to render self-feeding physically impossible. Its 

 long and narrow jaws, adapted to pierce the head of an 

 enemy, do not admit of being used for feeding, unless 

 liquid food is poured into them by the mouth of a slave. 

 This fact shows of how ancient an origin the instinct of 

 slave-making must be ; it has altered in an important 

 manner a structure which could not have been so altered 

 prior to the establishment of the instinct in question. 



Mr. Darwin thus sums up the differences in the offices 

 of the slaves in the nests of F. sanguined, and F. rufescens 

 respectively : 



The latter does not build its own nest, does not determine its 

 own migrations, does not collect food for itself or for its fellows, 

 and cannot even feed itself ; it is absolutely dependent on its nu- 

 merous slaves. Formica sanguinea, on the other hand, possesses 

 much fewer slaves, and in the early part of the summer extremely 

 few ; the masters determine when and where a new nest shall 

 l>e formed, and when they migrate, the masters carry the slaves. 

 Both in Switzerland and England the slaves seem to have the 

 exclusive care of the larvae, and the masters alone go on slave- 

 making expeditions. In Switzerland the slaves and masters 

 work together, making and bringing materials for the nest : 

 both, but chiefly the slaves, tend and milk, as it may be called, 

 their aphides ; and thus both collect food for the community. In 

 England the masters alone usually leave the nest to collect 

 building materials and food for themselves, their slaves and 

 larvae. So that the masters in this country receive much less 

 service from their slaves than they do in Switzerland. 



Mr. Darwin further observes that ' this difference in 

 the usual habits of the masters and slaves in the two 

 countries probably depends merely on the slaves being 

 captured in greater numbers in Switzerland than in Eng- 

 land ; ' and records that he has observed in a community 

 of the English species having an unusually large stock of 

 slaves that 'a few slaves mingled with their masters 



