DEVELOPMENT OF THE ALIMENTARY CANAL. 429 
In arriving at this conclusion, I have been guided by the 
fact that the rectal valve is similar to the proventriculus in the 
reduplication of the intestinal wall. It is well known that the 
latter is formed as an invagination, and I have frequently 
observed the distinct septum which separates the metenteron 
from the proctodeum (Pl. XXV., Fig. 6, s) both in dissections 
and in sections. 
The Malpighian vessels and ducts are at first outgrowths 
from the cells derived from Ganin’s ring (Pl. XXV., Fig. 2, m, mt), 
and the proximal intestine only appears at a later date as a 
thin straight transparent tube lined with columnar epithelium. 
The muscular coat of the intestine is first seen as a sphincter 
muscle close to the orifices of the Malpighian tubules, and then 
the canal connecting the proximal and distal intestines appears 
to be closed (Pl. XXV., Figs. g and 4). I have not been suc- 
cessful in obtaining a section in the proper plane to show the 
relation which subsists at this period between the lumen of 
the distal and proximal intestines; but if the intestine of a 
pupa is dissected out and examined, a slight pressure on the 
cover glass shows that the closure of the canal is due to 
the above-mentioned sphincter, and that there is no organic 
septum between the orifices of the Malpighian tubes and the 
proximal intestine. 
At a later period, or from about the seventh to the eighth day 
of the pupa, the distal intestine is filled and distended with a 
clear coagulable fluid precisely similar to that contained in the 
mesenteron; and judging from the appearance of the Mal- 
pighian tubes, they have not as yet commenced to pour any 
fluid into the intestine. They are quite twice the diameter 
they have subsequently, are perfectly cylindrical, and of a pale- 
yellow colour ; their cells contain both pigment granules and 
minute spherules of oil in great abundance. The latter are 
rendered intensely black by the action of osmium peroxide 
(Pl. XXV-, Fig. ¢). 
The rectal papilla have by this time attained very nearly 
their final stage of development, and the rectal pouch is filled 
with a milky fluid. This fluid is an emulsion of fine granules of 
