STEUCTUEE AND BIOLOGY OF SCHJZONEUEA LANIGEEA. 663 
V. The External Anatomy. 
The luteo'um ent. — The integfument consists of two 
layers — an outer, chitinous cuticle, and an inner, cellular, 
hypodennal layer, which produces the cuticle. 
The chitinous layer is thin and flexible, permitting free 
movement of the body segments. It is more stoutly deve- 
loped on the head and legs. The hypodermis consists of a 
layer of epithelium, in which are scattered small, oval nuclei, 
but cell boundaries are not clearly defined. 
Several small integumental bail's (7i.) are distributed over 
the body and legs. 
The Wax-secreting Glands (figs. 2 and 47). — Dis- 
ti-ibuted over the dorsal integument are numerous cir- 
cular or oval, facetted areas (iv. (/.) or plaques, the 
Wachsdriisenplatten of German authors. They are ar- 
ranged in transverse rows near the posterior borders of the 
thoracic and first seven abdominal segments, four on each 
segment. In addition, there are two on the eighth abdo- 
minal segment, and ten on the epicranial region of the head, 
the latter being situated on a thickened, quadrangular area 
of the cuticle, l}dng between the antenute. 
Each plaque consists of several polygonal areas surround- 
ing a central facette, beneath which are situated large glan- 
dular cells. When viewed in vertical section (fig. 47), each 
is seen to consist of a group of large, glandular cells (iv.c.), 
one cell under each polygonal facette. These cells form 
unicellular, dermal, wax-secreting glands, such as are found 
in many aphids (Pemphigus, Chernies, Lachnus, etc.), 
and considered by Claus (1867) to be specially modified 
hypodennal cells. Each of these glandular cells has a 
finely reticulate cytoplasm (cy.), and a prominent deeply 
staining nucleus (?t.) situated at the free end of the cell. At 
the base of each cell there is an irregular lumen (lu.), into 
which the waxy secretion is poured, being passed to the 
e.xterior as waxy filaments through the chitin of the polygomd 
areas. 
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