1934 ] 
Peritrophic Membrane in Sciara 
55 
honey-bee embryo, I was interested to see if there were 
any possible embryonic fore-runners of the peritrophic 
membrane. 
An examination of the slides indicated that the stomo- 
dseal invagination forms in the same manner as in Sciara. 
The cells in the floor of the invagination are a continuation 
of the ectoderm which forms the walls of the tube. The 
tube lengthens and widens at the end, the floor being re- 
duced to a thin membrane similar to that described above 
for Sciara. Late in the embryonic stage the inner walls of 
the stomodseum protrude into the mid-intestine rupturing 
the membrane. Around this invaginating tube lies a thick- 
ened ring of cells that resembles the ring of cells secreting 
the stomodseal membrane in Sciara. It also corresponds to 
the basal folds of the mid-gut as figured by Wigglesworth 
(’30) from which, he says, originates part of the peri- 
trophic membrane. Campbell (’29) has demonstrated the 
presence of chitin in the peritrophic membrane which is 
further proof that it arises from the ectoderm. A study of 
the first stage larva would undoubtedly yield more evidence 
but no larvae were available at the time this study was being 
made. 
Summary 
An examination of the oesophageal valve in both the em- 
bryological and the early larval stages of Sciara indicates 
that the peritrophic membrane is a continuation of the 
stomodseal membrane and is ectodermal in origin. It arises 
from a group of large secretory cells lying around the oeso- 
phageal valve and attached to the upper edge of the mid- 
intestine. These cells which are also ectodermal in origin, 
begin their development from the end of the stomodseum as 
it widens out and reverses its direction of growth. The 
large bulbous muscular layer of the oesophagus which en- 
closes the blood sinus, develops from the single layer of 
mesoderm which surrounds the stomodseum. 
In the honey-bee the formation of the stomodseum re- 
sembles the development in Sciara except that the stomo- 
dseal membrane does not attain such a great length but is 
