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 confirmed 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 sanguine, a, 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 
be 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 6 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 ; s 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 
