PARASITKS HIHKKXATIXO 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 larvoe of Zygobothria are similarly assumed to a definite 
petition, and in otherwise healthy caterpillars have invariably been 
found embedded in the walls of the crop, as indicated by figure 63. 
lu appearance they are typical of the tachinid first-stage larva? gen- 
erally, and with DO extraordinary points of difference from most 
others of the group to which they belong. Those of Compsilura 
(fig. 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 thai it should resemble the planidium of Perilam- 
pus. which, like Mesochorus. is a secondary parasite which gains 
access to its host before (he latter has left the body of the caterpillar 
which harbors both primary and secondary. It is 
presumed that it w ill be representative of a highly 
specialized type of development which fits it for 
the peculiar role which it plays, hut that this de- 
velopment will have been along wholly different 
lines from thai which has taken place in the Case 
of Perilampus. The w hole genus, apparent ly. pos- 
sesses habits similar to t hose of 1A sochorus pnll'iju s. 
A very beautiful and. according to Mr. Yiereck, an 
undescribed species has been reared from the 
COCOOnS of A pantries fiskci, parasitic upon a species 
of Parorgyia, under circumstances which indicate 
positively that attack was made while the pri- 
mary host was still alive. The same may be said 
of another undetermined species which has simi- 
larly been reared from Apanteles hyphantrix. 
Mesochorus paUipes is not an uncommon parasite of Apanteles 
lacieicolor 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 larvae. 
The female will undoubtedly attack parasitized as freely as it will 
Fig. (A.— Compsilura con- 
cinnata: First-stage lar- 
va. Oreatly enlarged. 
(Original.) 
