8 
Psyche 
[March - June 
are usually only half eaten. This may be due to the fact that in 
pulchellus the embryo is confined to the half of the seed which the 
ants eat, whereas in desvauxii the embryo extends more than three- 
quarters the length of the seed. 
As will be seen from the previous paragraphs, the major of militi- 
cida has a very limited part in the harvesting operations and even this 
small part can be handled equally well by the minors. It seemed 
unlikely that the major would be limited to so small a share in the 
activities of the colony. The first hint that they might perform some 
unique activity essential to the colony was provided by the majors 
who came out of the nests during baiting. The junior author, who 
spent much time at this work, noticed that before the major emerged 
from the nest it would often stand for a considerable period just in- 
side the nest entrance. When it did so it was a thorough nuisance 
to the minors, who had difficulty in getting past what amounted to 
a road block. When the major finally emerged from the nest it usu- 
ally opened its jaws to their fullest extent and made short lunges in 
the direction of small pebbles and bits of grass as though it were 
trying to bite them. Later it was found that this same lunging and 
biting response could be elicited by throwing a small beam of light 
into the opening before the major left it. It was further clear that 
the primary reason why the major left the nest was not hunger. They 
almost never went directly to the bait, but wandered around in their 
clumsy fashion as though they were looking for something else. 
It was only after considerable patrol that some of them would go to 
the bait. These responses suggested that the function of the major 
might be to guard the nest entrance and, to test this, a nest was con- 
structed which gave them the opportunity to do so. 
This nest consisted of two chambers connected by a single, long 
passage which could be blocked or unblocked in the middle without dis- 
turbing the nest. The block consisted of a cotton plug which could 
be pushed into the connecting passage through a glass tube set at 
right angles to it. With the plug in place the nest was divided into 
two separate chambers; with the plug removed the two chambers 
communicated with each other through the single connecting passage. 
After the plug was in place majors and minors of militicida were 
placed in one chamber and their prospective intruders in the other. 
The nest was then set aside until both groups were accustomed to 
their surroundings. Usually it took no more than twelve hours for 
each group to become thoroughly tranquil and to demonstrate by this 
tranquility that it was unaware of the other group’s presence nearby. 
