ANATOMY AND PHYSIOLOGY. 61 
ponent cells forcibly recall the structure of the cuticle 
of the higher animals ; and the rudiments of a three- 
fold division into cuticle, rete, and cutis agree with 
this comparison. But the functions of this integu- 
ment, so especially mechanical, and the permanent 
nature of the segmental sub-divisions, have more 
weight in the eyes of physiologists; and general 
opinion inclines to regard it as insect bone. 
The body of the larva is covered with a thin, soft 
membrane which has no more strength than is suffi- 
cient to retain the form of the almost diffluent 
embryo. But the lines by which this skin is in- 
dented, the thirteen segments into which it is divided, 
have a singular physiological importance. These 
segments are almost unvarying in number throughout 
the insect kingdom, the singular exception being 
found in the Hymenopterous order, with which we 
are now concerned, where a fourteenth segment 
occurs. They bear a definite relation to the parts 
of the perfect insect, and are all, as we shall see 
further on, more or less exactly represented there. 
The thin pellucid membrane which envelopes the 
wasp-grub has to undergo very important changes 
before it becomes the tegumentary skeleton of the 
perfect wasp. But the changes are all transacted 
within the cell. When the insect emerges from the 
cocoon her skin is as perfect and as changeless as the 
rest of her structure. The integuments need only 
to harden and dry, and have their colours brought 
out by the light, to become such as they are to con- 
tinue for life. : 
As this covering cannot grow, so neither can 
there be any growth of the insect. A wasp may 
