PEEIPLANETA ORIENTALIS. 
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It is clear from the above description that these pouches are 
merely invaginations of the body wall between the terga, round 
which the hypodermis has greatly proliferated, and this is 
borne out by their development. Fig. 4 represents a section 
from a larva of about 8 mm. in length; there is a slight de- 
pression lined by a few chitinous hairs, which are branched 
at the base, and the cells of the upper layer are somewhat 
crowded. There are only two of the large columnar cells 
to be seen ( l . 1.), which are here rounded, and probably become 
columnar by flattening against one another. A series of 
gradations can easily be made out between this early stage 
and the adult stage shown in fig. 2. The fact of the hairs 
being branched at the base, and the crowding of the upper 
layer, seems to indicate that the hairs develop as simple foldings 
of the cuticle. The lower columnar cells seem to be modified 
hypodermic cells, but it should be noticed that they have a 
distinct nucleolus, which I have been unable to make out in 
other hypodermic cells ; in fact their nuclei exactly resemble 
in shape, size, and appearance those of the fat-bodies. 
As to the function of this organ, I have no doubt that it is 
glandular, and it is probable that it is a stink-gland, though I 
have not been able to satisfy myself of this. The interior of 
each pouch is usually filled with granular matter, which stains 
with haematoxylin but not with borax carmine. I have no 
doubt this is the secretion. The function of the hairs, into 
which the secretion must in the first place pass, may perhaps 
be to act as ducts, and at the same time to diffuse the odour 
by offering a larger surface for evaporation. 
Structure of the Hypodermis. — Miall and Denny, in 
their valuable work on ‘the Cockroach/ describe the hypo- 
dermis as a single layer of cells, each cell corresponding to 
a polygonal area of the chitinous cuticle, and resting on a 
basement membrane. Below this are described here and there 
large nerve-end cells which send up fine processes into sensory 
hairs on the upper surface. I am unable, however, to agree 
with this description as far as the dorsal sui’face is concerned. 
From my sections (see figs. 2 and 4) I find the hypodermis, in 
