May 24,1924 Polyembryonic Development of Platygaster vernalis 
837 
to cleavage of daughter germs. A similar condition obtains for some of the 
blastulas, but the instances are rare. Occasionally a group of three or four blas- 
tulas will fail to continue development. Examination of the parasite body shows 
in such instances that a portion of it has become separated in the host intestine 
from the rest of the parasite body, and that the detached portion did not happen 
to become provided with a sufficient amount of the trophamnion and paranu¬ 
clear masses. Such blastulas then become aborted. 
Occasionally host larvte are met with which contain more than one parasite 
body, in spite of the tendency of the parasite to oviposit in an egg only once, 
and to deposit at that time only a single egg. At such times one of the parasite 
eggs may fail to continue development. An undeveloped parasite body of this 
kind is illustrated in Plate 4, D. 
Aborted eggs, germs, blastulas, or larvae in Platygaster vernalis are rare in 
comparison to those which have been observed in Copidosoma gelechiae and in 
< 7 . truncatellum , a condition which is to be expected in polyembryonic insects 
which show a comparatively simple type of polyembryonic development. 
THE LARVA 
As has been shown by the junior writer ( 1 , 2) the larva passes through two 
distinct stages in completing its development. When the insect takes its first 
food it is known as the primary larva (PI. 8, A). In this stage the larva is elongate 
oval, bluntly rounded at both ends, and possesses two relatively large mandibles. 
This stage is further characterized by a lack of distinct body segmentation, and 
the presence of two very prominent lateral knoblike projections which are 
located in the head region at the base of the mandibles. The primary larva 
measures about 0.54 mm. in length and 0.18 mm. in width. 
The mature larva (PI. 8, B, C) is white, ovoid, and measures about 1 mm. in 
length and 0.5 mm. in width. Spiracles are present in this stage on the second 
and third thoracic segments, and second abdominal segment only. The man¬ 
dibles of the mature larva are less than half the length of those of the primary 
larva. Eleven distinct body segments are defined in the mature larva. 
Feeding commences when the primary larva is fully formed. The larvae of a 
brood first consume the remnants of the trophamnion, whereupon they become 
liberated in the mid-intestine of the host (PI. 1, D) and ingest the chyle. The 
intestine is next ruptured and the fatty tissues consumed. In the course of 
feeding, the entire contents of the host larva are consumed, leaving only the outer 
cuticle (PI. 8, C) to contain the fully developed parasite larvae. In the process of 
feeding, the superior lip is moved toward and away from the inferior lip by 
radiating muscles which are quite prominent in the head region. 
A parasitized larva very seldom succeeds in pupating, but it does form the 
puparium. Each parasite larva, when fully grown, forms a cocoon, so that a, 
brood of the parasites in the larval or pupal stages is contained within a cluster 
of cocoons (PI. 1, E), which is in turn confined in the puparium of the host (PI. 
1, F). 
THE PUPA 
The pupa (PI. 8, D) is formed in the cocoon. At the time of transformation 
it is white in color, but gradually the eyes and body darken until it is a shiny 
black. The parasites^spend two to three weeks in the pupal stage. 
THE ADULT 
The adult is shiny black and measures from 0.7 to 0.9 mm. in length. An 
average of about eight individuals, which are nearly always of the same sex, 
are reared from one host. After emergence in spring they will live in confinement 
