22 Chapter I. 



as have ventured too far, are seized and killed by 

 crowds of the assailed. 



If with higher animals it is a mark of intelligence 

 to "utilize the senses of all for the protection of the 

 commonwealth," the same must be said of ants, and 

 in a more perfect degree. The posting of sentinels 

 for the protection of the community may be observed 

 with these social insects just as well, and even better 

 than with the social apes. In a nest of Formica san- 

 guinea comprising four species of slaves (or auxil- 

 iaries), namely, F. fusca, rufibarbis, rnfa and pra- 

 tensis, which is under my observation for many years, 

 I can verify this fact every day. We subjoin a 

 diagram of this observation nest, as it will often be 

 referred to in the sequel. 



The main nest and its annex are made of glass 

 plates in wooden frames. The space between the two 

 plates in each nest is partly filled with earth, their 

 vertical distance being from 10 to 12 millimeters, so 

 that the ants have freedom of motion to perform their 

 work without being able to screen themselves from 

 observation. The upper glass plate is generally cov- 

 ered with a black cloth ; for if light were permitted 

 to enter, the ants would coat the lower surface of the 

 glass with earth in order to darken the interior of 

 the nest. By means of glass tubes the main nest and 

 its annex are put in communication with each other 

 and with the other parts of the nest, which are like- 

 wise of glass. (See diagram.) 



In the main nest, which corresponds to the interior 

 of an ordinary ant nest, the majority of the ants are 

 to be found with their queens, their larvae, pupae and 



