PARASITES HIBERNATING IN BROWN-TAIL WEBS. 265 
canal, its axis parallel to the axis of the body of the host caterpillar, 
and its head in the ultimate or penultimate body segment, and 
pointed toward the rear. 
The larve of Zygobothria are similarly assigned to a definite 
position, and in otherwise healthy caterpillars have invariably been 
found embedded in the walls of the crop, as indicated by figure 63. 
In appearance they are typical of the tachinid first-stage larve gen- 
erally, and with no extraordinary points of difference from most 
others of the group to which they belong. Those of Compsilura 
(fic. 64) may be found in similar positions, but they are easily dis- 
tinguishable from Zygobothria by the presence of the three chitinous 
anal hooks or spines, as indicated in the accompanying figure. 
Nothing is known of the hibernating stage of Mesochorus. It does 
not seem probable that it should resemble the planidium of Perilam- 
pus, which, like Mesochorus, is a secondary parasite which gains 
access to its host before the latter has left the body of the caterpillar 
which harbors both primary and secondary. It is 
presumed that it will be representative of a highly 
specialized type of development which fits it for 
the peculiar role which it plays, but that this de- 
velopment will have been along wholly different 
lines from that which has taken place in the case 
of Perilampus. The whole genus, apparently, pos- 
sesses habits similar to those of Wesochorus pallipes. 
A very beautiful and, according to Mr. Viereck, an 
undescribed species has been reared from the 
cocoons of Apanteles fiskei, parasitic upon a species 
of Parorgyia, under circumstances which indicate 
positively that attack was made while the pri- ,,, POURS Se aol 
mary host was still alive. The same may be said _ cinnata: First-stage lar- 
of another undetermined species which has simi- eda, aneaaiee 
larly been reared from Apanteles hyphantriez. 
Mesochorus pallipes is not an uncommon parasite of Apanteles 
lactevcolor Vier., having been reared from only a few among the many 
localities from which its host has been secured in numbers, but the 
average proportion of parasitized individuals has been only about 
2 per cent. 
The interrelations of these several parasites thus closely associated 
with one stage of the same host, and consequently with each other, 
are interesting and peculiar. Pteromalus, of course, cares little 
whether the host caterpillar selected for attack is parasitized by 
one or more of the endoparasites which hibernate as first-stage larve. 
The female will undoubtedly attack parasitized as freely as it will 
