PATTERNS IN THE INTEGUMENT OF INSECTS
43
of the hormonal and nutritional milieu. The complexity of interactions
between cells is severely limited by the arrangement of the cells in a
single layer. Problems of local differentiation are reviewed in Wigglesworth (1959) and will not be considered here.
C. Humoral Control
The general picture of the humoral control of epidermal events is clear
from classical insect physiology (Wigglesworth, 1954b). The brain is
stimulated in various ways to release the thoracotropic hormone which
stimulates the prothoracic gland to produce the molting hormone causing
molting. Molting in the presence of the juvenile hormone from the
corpus allatum ensures that new structures are of larval form. In the
absence of juvenile hormone, adult characters appear at molting. This
field has been extensively reviewed (see, for example, Gilbert, 1964).
Several problems of cuticular morphogenesis can only be understood in
relation to the hormonal control of the epidermis, but only those problems of hormonal control most clearly affecting cuticular patterns will
be considered further here.
The molting hormone initiates molting. Thereafter, the main sequence
of events is determined intrinsically from within the responding epidermal
cells. However, some events at molting (hardening and darkening, Cottrel, 1962a-e; Fraenkel and Hsaio, 1962), and intermolt events (wax
secretion, Locke, 1965b; the deposition of lamellate cuticle and the frequency of lamellae, Condoulis and Locke, 1966; the diurnal rhythm of
protein deposition, Neville, 1963a-c) are extrinsically controlled through
hormones and/or nutrition.
The level of juvenile hormone influences: (1) the differentiation of
epidermal cells to bristles, scales, etc., (2) the type of cuticle and the
surface pattern, and (3) cell death.
II. Problems in Pattern Formation
In the formation of the integument, we can distinguish several types
of pattern and problems. At the molecular level there are problems posed
by the arrays of fibrous chitin-protein polymers, lipid-water liquid crystals, and the de novo origin of the plasma membranelike structure of
the cuticulin. At the level of single cells, there are the irreversible changes
of differentiation. The massive cell destruction which takes place at
metamorphosis can be thought of as a special case of differentiation. In
groups of cells, there are problems of intercommunication of information
about orientation and the regulation of size, and in the whole organism
the cyclical changes of hormone level in time are translated to phases of
secretion recorded in the three-dimensional pattern of cuticle deposition.
43
of the hormonal and nutritional milieu. The complexity of interactions
between cells is severely limited by the arrangement of the cells in a
single layer. Problems of local differentiation are reviewed in Wigglesworth (1959) and will not be considered here.
C. Humoral Control
The general picture of the humoral control of epidermal events is clear
from classical insect physiology (Wigglesworth, 1954b). The brain is
stimulated in various ways to release the thoracotropic hormone which
stimulates the prothoracic gland to produce the molting hormone causing
molting. Molting in the presence of the juvenile hormone from the
corpus allatum ensures that new structures are of larval form. In the
absence of juvenile hormone, adult characters appear at molting. This
field has been extensively reviewed (see, for example, Gilbert, 1964).
Several problems of cuticular morphogenesis can only be understood in
relation to the hormonal control of the epidermis, but only those problems of hormonal control most clearly affecting cuticular patterns will
be considered further here.
The molting hormone initiates molting. Thereafter, the main sequence
of events is determined intrinsically from within the responding epidermal
cells. However, some events at molting (hardening and darkening, Cottrel, 1962a-e; Fraenkel and Hsaio, 1962), and intermolt events (wax
secretion, Locke, 1965b; the deposition of lamellate cuticle and the frequency of lamellae, Condoulis and Locke, 1966; the diurnal rhythm of
protein deposition, Neville, 1963a-c) are extrinsically controlled through
hormones and/or nutrition.
The level of juvenile hormone influences: (1) the differentiation of
epidermal cells to bristles, scales, etc., (2) the type of cuticle and the
surface pattern, and (3) cell death.
II. Problems in Pattern Formation
In the formation of the integument, we can distinguish several types
of pattern and problems. At the molecular level there are problems posed
by the arrays of fibrous chitin-protein polymers, lipid-water liquid crystals, and the de novo origin of the plasma membranelike structure of
the cuticulin. At the level of single cells, there are the irreversible changes
of differentiation. The massive cell destruction which takes place at
metamorphosis can be thought of as a special case of differentiation. In
groups of cells, there are problems of intercommunication of information
about orientation and the regulation of size, and in the whole organism
the cyclical changes of hormone level in time are translated to phases of
secretion recorded in the three-dimensional pattern of cuticle deposition.