164 Schrader. 
produce males”. SHINJI (1919), on the other hand, assumes that 
fertilization occurs; but seemingly he has not considered any other 
possibility, for, speaking of a large central nucleus in the egg, he states 
somewhat naively: “Since this large nucleus divides it must be the 
first cleavage nucleus. It follows therefore, that the union of the male 
and female pronuclei must have occurred during the passage of the 
ege pronucleus to the center of the egg after the formation of the last 
polar body.” 
The belief that parthenogenesis occurs is strengthened by the 
fact that the early stages of development take place in the body of 
the mother, and that very commonly many embryos have simultaneously 
reached an advanced stage in the formation of the germ band when 
the eggs are extruded. Although this condition might be considered 
as good evidence for parthenogenesis in other insects, the morpho- 
logy of the reproductive organs makes it clear that fertilization of 
all the eggs may very easily occur in Pseudococeus. The ovary 
comprises two ducts which unite distally. Directly attached to each 
duct at short intervals are the ova, each with a certain number of 
nurse cells (EMEIS, 1915). In females of the later instars, sperms are 
found throughout the entire length of the duct, making it possible for 
each egg to be fertilized in situ as maturity is reached. Development 
may thus begin without necessitating passage of the egg down the 
oviduct past the spermatheca, as is the case in nearly all other insects 
where fertilization occurs. 
It was evident that a careful investigation was necessary. The 
most natural method of settling the question of parthenogenesis was 
by breeding experiments. The point to be established first of all was 
whether virgin females give rise to offspring. The breeding experiments, 
simple though they were in their conception, presented various diffi- 
culties. To obtain unfertilized females, larvae just hatched from eggs 
were isolated on plants which -had previously been treated with 
insecticide and washed. Such larvae had to be picked at random, for 
at the early stage indicated, there were found no ‚external indications 
of a sex differentiation. Isolation was accomplished by keeping the 
host plant under a lamp chimney covered with silk bolting cloth (180 
meshes per inch). The latter precaution was necessary because larvae 
of the first instar are surprisingly active. As I soon found, they often 
make their way through ordinary gauze which of course opens the way 
to contamination from the outside. Although the use of fine bolting 
