84
MICHAEL LOCKE
in the target cells. In studying the hormonal mechanism of control of
the sequence of these syntheses, we may have a useful tool for attacking
the problem posed by intrinsically determined sequences of syntheses
in general.
2. Diurnal Rhythms of Deposition in the Cuticle
Neville (1963c) has shown that insects from a number of orders lay
down the cuticle below the epicuticle in a series of daily growth layers.
In transverse sections of the tibia and other appendages, alternating
dark and light bands can be made out when viewed between crossed
polaroids. In Decticus for example, two light bands alternate with a
dark band in the preecdysial cuticle, thereafter each daily interval is
marked by a pair of bands, one light and one dark. These bands can
also be made out by phase contrast. The relation between these bands
in the tibiae and growth layers in other sorts of cuticle is not yet clear.
The difference in birefringence could be due to a variable incorporation
of protein masking the birefringence of the chitin, or it could be due
to a change in orientation.
In the wing hinges of locusts and in solid cuticle elsewhere (Neville,
1963a,b), the daily rhythm of growth is superimposed upon microcycles
of lamellar deposition (Fig. 1). When viewed by ultraviolet light there
are alternating dark and light regions of fluorescence. A wide brightly
fluorescent layer is formed each night and a thin faintly fluorescent
zone is formed by day. Experimentally prolonged days and nights induced corresponding changes in the width of these zones. The alternating
fluorescence may be due to variations in the synthesis of two amino
acids which link resilin chains together (Andersen, 1963).
8. Microcycles in the Deposition of Lamellate Cuticle
The chitin-protein fibers immediately below the epicuticle may be
irregular (Fig. 3), but this soon changes to arrays of fibers ordered in
lamellae (Figs. 4 and 5). Some lamellae are laid down before ecdysis, but
in many insects the bulk of the cuticle is deposited later in the stadium
as the animal feeds, forming a nutritional reserve called upon at the
next molt. Growth is partly by intussusception between previously formed
lamellae (Condoulis and Locke, 1966) and partly by the addition of
new lamellae. The formation of the major part of the cuticle as a succession of layers is of general occurrence in arthropods, and is usually
independent of the exact nature of the protein component and subsequent processes concerned in stabilization. We can think of the lamellae
as microcycles of deposition which record in space the previous synthetic
and orienting activity of the cells in time.
MICHAEL LOCKE
in the target cells. In studying the hormonal mechanism of control of
the sequence of these syntheses, we may have a useful tool for attacking
the problem posed by intrinsically determined sequences of syntheses
in general.
2. Diurnal Rhythms of Deposition in the Cuticle
Neville (1963c) has shown that insects from a number of orders lay
down the cuticle below the epicuticle in a series of daily growth layers.
In transverse sections of the tibia and other appendages, alternating
dark and light bands can be made out when viewed between crossed
polaroids. In Decticus for example, two light bands alternate with a
dark band in the preecdysial cuticle, thereafter each daily interval is
marked by a pair of bands, one light and one dark. These bands can
also be made out by phase contrast. The relation between these bands
in the tibiae and growth layers in other sorts of cuticle is not yet clear.
The difference in birefringence could be due to a variable incorporation
of protein masking the birefringence of the chitin, or it could be due
to a change in orientation.
In the wing hinges of locusts and in solid cuticle elsewhere (Neville,
1963a,b), the daily rhythm of growth is superimposed upon microcycles
of lamellar deposition (Fig. 1). When viewed by ultraviolet light there
are alternating dark and light regions of fluorescence. A wide brightly
fluorescent layer is formed each night and a thin faintly fluorescent
zone is formed by day. Experimentally prolonged days and nights induced corresponding changes in the width of these zones. The alternating
fluorescence may be due to variations in the synthesis of two amino
acids which link resilin chains together (Andersen, 1963).
8. Microcycles in the Deposition of Lamellate Cuticle
The chitin-protein fibers immediately below the epicuticle may be
irregular (Fig. 3), but this soon changes to arrays of fibers ordered in
lamellae (Figs. 4 and 5). Some lamellae are laid down before ecdysis, but
in many insects the bulk of the cuticle is deposited later in the stadium
as the animal feeds, forming a nutritional reserve called upon at the
next molt. Growth is partly by intussusception between previously formed
lamellae (Condoulis and Locke, 1966) and partly by the addition of
new lamellae. The formation of the major part of the cuticle as a succession of layers is of general occurrence in arthropods, and is usually
independent of the exact nature of the protein component and subsequent processes concerned in stabilization. We can think of the lamellae
as microcycles of deposition which record in space the previous synthetic
and orienting activity of the cells in time.