No. 420.] AN EXTRAORDINARY ANT-GUEST. 1013 
Reflection shows that the position of the puparium in the 
posterior pole of the cocoon, though the reverse of the position 
of the larval commensal with respect to its larval host, is the 
only one which can be maintained by the commensal with per- 
fect safety. Like other ants, the Pachycondyla leaves its cocoon 
through a rent in the anterior pole. This rent is certainly made 
by the mandibles of the hatching ant, and it is possible that the 
callow insect may succeed in making its way out of the cocoon 
without any assistance from the workers. I have hitherto 
failed, however, to surprise one of these ants in the act of 
hatching. But even if the obstetrical aid of the workers is 
necessary, as it is in the more highly specialized Camponotinz, 
any position for the commensal puparium, except at the poste- 
rior pole of the cocoon, might be fatal, for the struggling jaws 
and legs of the emerging ant and the jaws of the assisting ants 
would certainly be very liable to cut into any delicate object 
attached to the anterior or median walls of the cocoon. This 
danger, of course, would not exist if the fly hatches before the 
ant and is able to perforate the cocoon and escape. It is alto- 
gether more probable, however, that the ant hatches before the 
fly in the manner suggested below. 
It would be interesting to know what the commensal larva is 
doing while the ant-larva is weaving its cocoon. Does it move 
about to avoid the swaying jaws of the spinning larva? or does 
it take up its position from the first at the posterior end of 
the larval ant and there remain motionless while the posterior 
pole of the cocoon is being completed? It is very difficult to 
answer these questions. The fact that the posterior poles of 
all the cocoons containing puparia were somewhat distorted, 
being broader, more obtuse, and more irregular than the normal 
cocoons, would seem to indicate that the ant-larva may modify 
this end of its cocoon for the better accommodation of the com- 
mensal. I am inclined to believe, however, that the distortion 
may be produced by the dipteron larva while attaching itself 
just before pupating to the newly woven and still plastic cocoon. 
At this point my observations end. The phorid puparia 
were kept for several weeks in what I supposed to be the 
proper conditions of warmth and moisture, but to my intense 
