20 WORKERS—SOLDIERS. 
tion, and a second with immense heads provided with 
very large jaws. This differentiation of certain indi- 
viduals so as to adapt them to special functions seems 
to me very remarkable; for it must be remembered 
that the difference is not one of age or sex. The large- 
headed individuals are generally supposed to act as 
soldiers, and the size of the head enables the muscles 
which move the jaws to be of unusual dimensions; but 
the little workers are also very pugnacious. Indeed, 
in some nests of Pheidole megacephala, which I had 
for some time under observation, the small workers 
were quite as ready to fight as the large ones. 
Again, in the genus Colubopsis Emery discovered 
that two ants, then supposed to be different species, and 
known as Colobopsis truncata and C. fuscvpes, are really 
only two forms of one species. In this case the entrance 
to the nest is guarded by the large-headed form, which 
may therefore fairly be called a soldier. i 
Savage observed among the Driver Ants, where also 
there are two kinds of workers, that the large ones 
arranged themselves on each side of the column formed 
by the small ones. They acted, he says, evidently the 
part of guides rather than of guards. At times they 
place ‘their abdomen horizontally on the ground, and 
laying hold of fixed points with their hind feet (which 
together thus acted as a fulcrum), elevate the anterior 
portion of their bodies to the highest point, open wide 
their jaws, and stretch forth their antenne, which for 
the most part were fixed, as if in the act of listening 
