838 
Journal of Agricultural Research 
Vol. XXVIIJ, No. 8 
from three to twenty-nine days, the length of time depending upon the food and 
the humidity of the atmosphere. 
Oviposition by fertilized or unfertilized females takes place immediately after 
emergence if the parasite happens to come in contact with a host egg. Experi¬ 
ments conducted by the junior writer {#) show a definite tendency for a female 
to oviposit only once in a host egg. The preparations, studied by the writers, 
which resulted from ovipositions controlled in the laboratory, indicate conclu¬ 
sively that a single egg is deposited at each oviposition. 
SEX RATIO 
A study of the sex of individuals of the broods indicates that usually all of a 
brood are either males or all females. Of 48 broods, 40 were either pure male or 
pure female broods, and 8 were mixed. A similar ratio has been shown by Mar- 
chal ( 5 ) for Polygnotus minutus; in the article cited he records the sex of 16 
broods; eight being pure female broods, six male broods, and two mixed. Mar- 
chal believes that a mixed brood originates as a result of a fertilized and an un¬ 
fertilized egg being deposited in the host. The writers believe that a similar 
explanation will answer for Platygaster vernalis. 
SUMMARY 
(1) Platygaster vernalis develops polyembryonically in the larva of the Hessian 
fly, one egg giving rise eventually to approximately eight individuals. There is 
but one generation annually. 
(2) The adult parasites emerge from their cocoons in spring and almost imme- 
. diately oviposit in the eggs of the host. By the first of June the embryos are 
fully formed in a well-grown host larva. The larvae feed upon the host during 
June and July, and then transform to pupae, which in turn become adults in 
August. 
(3) A single egg is deposited by the parasite at each oviposition, and in such a 
manner that the egg always becomes lodged in the host’s mid-intestine, where 
development to the larval stage is completed. Development begins immediately, 
whether the egg is fertilized or unfertilized. 
(4) If more than one egg is deposited in the same host by different females 
one of the eggs may become aborted. 
(5) In the course of maturation two polar bodies are formed, which become the 
two original paranuclear masses. The maturated oocyte or cleavage nucleus 
becomes the progenitor of the embryos. 
(6) Four divisions of either the conjugated or parthenogenetic cleavage 
nucleus result in the production of twelve to sixteen embryonic nuclei, each of 
which apparently gives rise to a germ. The germs develop in the central part of 
the parasite body and are encompassed b}^ the trophamnion containing paranu¬ 
clear masses. 
(7) Some of the germs divide once, at the time they are composed of eight 
nuclei, to form two daughter germs. A further division of the daughter germs 
apparently results in the production of pseudogerms. 
(8) The group of germs comprising a parasite body is known as a polygerm. 
Each normal germ passes through the blastula and late embryonic stages, and 
finally becomes a primary larva. During the course of this development the 
parasite body increases in size and remains intact in the mid-intestine of the host. 
(9) When the primary larvae are formed they rupture the thin trophamniotic 
membrane and begin to feed upon the contents of the host’s mid-intestine. Later 
the mid-intestine is ruptured, whereupon the secondary or mature larvae devour 
the entire contents of the host, leaving only the cuticula. 
