IOI2 THE AMERICAN NATURALIST. (Vor. XXXV. 
which contained pseudonymphs of Pachycondyla and were, there- 
fore, of recent formation, commensals were found! Having 
shared the table of their host, they had come to share its bed as 
well. The dipteron, too, had pupated after the manner of its 
kind — forming a puparium ; z.e., instead of spinning a cocoon 
like the ant-larva, the dead larval skin, somewhat shriveled and 
contracted, was used as an envelope, and within this the pupa 
proper was formed. 
This puparium, represented in Fig. 2, is from 2.25 to 2.5 mm. 
long and clearly of the cyclorhaph type. It is elliptical, much 
flattened dorso-ventrally, especially 
along the edges, which are thin and 
hyaline andalmost alate. The brown- 
ish dorsal surface is thrown into deli- 
cate and irregular transverse wrinkles. 
Anteriorly, in the thoracic region, 
there is a pair of short black res- 
piratory tubes. The ventral surface 
is very glabrous and distinctly paler 
than the dorsal surface. From its 
small size, cyclorhaphous character, 
and resemblance to the puparium of 
a typical Phora bred by one of my 
: assistants, Mr. C. T. Brues, from 
Fic. 2.—Puparium of phorid com- Some spider's eggs, I conclude that 
mensal from ae cocoon of Pachy- . . . 
debis Mer the insect under consideration must 
be one of the Phoridæ. 
Subsequently, several other cocoons were opened and two 
more were found to contain the puparia of commensals. In all 
four cases the puparium was invariably located in the caudal 
pole of the cocoon, just to one side of the black blotch of ejecta 
deposited by the ant-larva before becoming a pseudonymph. 
At this point the puparium was immovably stuck to the wall of 
the cocoon by means of its smooth ventral surface. Its anterior 
end was directed towards the cephalic pole. As there is always 
considerable space, especially at the posterior pole, between 
the walls of the cocoon and the enclosed ant-pupa, the much- 
flattened fly puparium did not in the least crowd its host. 
