IOIA4 THE AMERICAN NATURALIST. [Vor. XXXV. 
disappointment they failed to hatch. During the autumn and 
winter frequent and diligent search was made for more of the 
commensals in all the Pachycondyla nests I could find, but in 
vain. Finally, during the latter part of May of the current 
year, I discovered in a very different locality two Pachycondyla : 
nests which contained a few phorid larva. This discovery 
proved that the phorid is double-brooded like its host. But 
the larvae were very small and attached to such very young 
ant-larvee that I despaired of being able to raise them in my 
artificial nests as far as the imaginal stage. It remains, there- 
fore, for the future to fill this gap in my observations. 
As a small contribution towards filling this gap I venture to 
advance the following conjecture concerning the circumstances 
under which the phorid fly probably hatches. I assume that 
the ant must hatch before the fly. Now very soon after the 
former hatches the useless cocoon is always carried by a worker 
and placed on the refuse heap, which in the natural nest is 
often almost entirely made up of the empty cocoons of from 
one to several broods of ants, and lies in a rather dry and well- 
ventilated spot immediately beneath the stone covering the 
nest. Along with the cocoon is carried the phorid puparium 
still adhering to the wall at its unopened posterior end. Thus 
after a privileged existence as free pensioner and bedfellow to a 
generous host, it is unwittingly carried away in the worn-out 
bedclothes and consigned to the family rag pile. Here the 
small and probably very active fly hatches, leaves by the wide- 
open front door of the cocoon, and, after mating, either returns 
to lay a few eggs in the galleries of its former host, or flies 
away to oviposit in some other Pachycondyla nest. Thus the 
simple assumption that the fly hatches later than the ant 
renders it unnecessary to suppose that the fly possesses some 
peculiar means of perforating the tough wall of the cocoon, 
and also accounts for the position of the puparium in the pos- 
terior pole, where it would be completely concealed from the 
workers even after the escape of the callow ant. 
In conclusion the reader’s attention may be directed to cer- 
tain particulars of special interest in connection with the life 
history of the Pachycondyla commensal: 
