DEVELOPMENT OF A HYMENOPTEROUS PARASITE 535 
tubercles at the extreme anterior edge of the body and a pair of 
large projecting chitinized mandibles separated by the funnel- 
shaped mouth opening. The body is not heavily chitinized. 
The oesophagus is short and leads abruptly into the large sac- 
like mesenteron which fills the greater part of the body. The 
proctenteron appears as a tenuous cord of cells without a lumen 
and terminating in a small anal opening on the ventral side of 
the last segment. 
The planidium larva is very active, moving rapidly over the 
dorsum of the host’s abdomen, apparently searching for a place 
to insert its chitinous mandibles. In its habits it closely re- 
sembles the planidium of Orasema viridis Ashmead and the ex- 
ternal planidium of Perilampus hyalinus Say, though I was not 
able to find ambulatory spines upon its body. It was never 
observed to enter the host’s body as is the habit with Perilampus, 
but was found to be an ectoparasite throughout its entire life 
history. Nor have I ever seen it anywhere except upon the 
dorsum or dorso-lateral surfaces of the host’s abdomen, and 
owing to the thick, chitinous integument of the fly pupa at every 
point except the abdomen, it is doubtful whether it could else- 
where gain access to its food. Having inserted its mandibles 
into the dorsal abdominal integument of its pupal host, it begins 
to grow and steadily increases in all dimensions. It is probable 
that an ecdysis takes place just before it passes over into the 
atracheate larval stage, but this was not definitely observed. 
THE ATRACHEATE LARVA 
Within three to five days after leaving the egg, the planidium 
reaches the atracheate stage. It is distinguished from the pre- 
ceding by its larger size and the condition of the mandibles which 
are proportionally reduced and do not protrude beyond the 
mouth opening. The length varies somewhat, but is approxi- 
mately 2 mm.; the greatest breadth is about 50 per cent of the 
length, showing a marked increase in bulk over that of the 
planidium. Thirteen segments are visible, the first being some- 
what reduced, the second largest. The antennal tubercles can 
