ME TAMORPHOSIS, 
101 
the mouth and anal extremities by invagination of 
the external skin (Fig. 57, c), the yolk separating the 
anterior and posterior portions of the intestine. The 
middle or central portion forms the yolk sac. and later 
the separating walls undergo absorption, forming a 
single and united tube. The annexed organs are then 
added to this intestine, which forms prolongations of 
the wall. In this manner the salivary glands are also 
formed from the silk glands in the larva at the anterior 
part, and at the posterior the malpighian tubes, or 
urinary organs. An arrested development in the larvae 
of bees, hornets, and wasps, causes the middle in- 
testine to remain blind, so that the larva in the cell 
passes no dejections, which were it otherwise, under 
the conditions of its existence, would be an embar- 
rassment. The manner in which the bowel is cast 
has been explained in Chapter ii., page ii. 
As the abdomen acquires its shape, the sting, 
as we have already seen, first outside, becomes in- 
ternal on the infolding of the anal region, and at 
the same time new muscles and tendons are 
formed. 
The development of the wings has occupied the 
attention of many scientists, amongst whom we may 
mention Swammerdam (158), Burmeister (17), Pan- 
critius (122), Landois (87), Girard (47), Rehberg 
(141), and others. Girard says the wing is formed 
from a vesicle, or flattened pouch, supported in the in- 
terior by a framework of tubes of chitine, which form 
the nervures ; when, by re-absorption of the contained 
fluid, the two membranes are intimately joined, they 
M 
