198 
Journal of Agricultural Research 
Vol. XIV, No. 5 
head directed toward the caudal end of the caterpillar. After 2 or 3 
days the parasite passes into the third stage (PI. 21, A); the mandibles 
of this stage differ markedly from those of either of the other stages, 
being much longer and pectinate (PI. 20, E). In the third stage the larva 
possesses a tracheal system, not evident before. In this stage, too, the 
anal vesicle begins to be reinvaginated, being gradually drawn back into 
the body of the larva, so that, when the parasite issues, no vesicle can be 
seen. 
The infested brown-tail-moth caterpillars are very noticeably retarded 
and do not get beyond the stage in which they hibernated. Death occurs 
in from 7 to 12 days after they have begun feeding, and very shortly the 
full-grown parasitic larva issues. 
The species of Apanteles commonly do not kill their hosts upon issuing, 
the latter sometimes remaining alive two weeks or more. The death of 
the victims of A. lacteicolor then, just prior to issuance of the parasite, is 
interesting. Just how this death of the host is brought about is not 
certainly known; but the writer found, on dissecting caterpillars from 
which this parasite had just issued, that the central nervous system in 
the posterior part of the body was entirely destroyed, while in various 
caterpillars, still living, deserted by other species of Apanteles, no such * 
injury had taken place. That in the former case destruction of the 
nenrtms system occurs not more than a few hours before the issuance of 
the parasite, was determined as the result of dissecting a number of 
brown-tail-moth caterpillars containing A. lacteicolor larvae almost ready 
to issue, these caterpillars being still alive; the nervous system in these 
cases had not yet been injured. It seems very probable, after these 
observations, that the destruction of the nervous system by the larvae 
of A. lacteicolor is responsible for the early death of the hosts of this 
parasite. 
COCOON Off APANTELES LACTEICOLOR 
Directly upon issuing from its host, the larva of A . lacteicolor begins 
spinning its cocoon, completing this after three hours or more. The 
process of spinning consists of a continuous looping of the silken thread 
as this is spun out, and a careful fastening of these loops; the larva finds 
it necessary, in the course of this work, to reverse its position many times. 
When complete the cocoon is pure white, oblong-cylindrical in form, 
4 to 4.5 mm. in length, and surrounded by a small amount of loose silk. 
The cocoons of the wintering generation are commonly found in the 
webs of the brown-tail moth caterpillars, while those of the summer 
generations occur on the underside of leaves, in crevices of the bark, etc. 
Changes within the cocoon are rapid. From 18 to 24 hours after 
spinning has ceased, the waste matter that has accumulated in the mid¬ 
intestine during endoparasitic life (the caudal end of the midintestine 
is closed during this period) is excreted and is forced to the end of the 
cocoon. Pupation takes place about 48 hours after the larva has ceased 
