52
MICHAEL LOCKE
remaining expansion in the axis can only be relieved by the formation
of fine transverse folds.
We can think of hierarchies of stresses, restraints, and deformation
which set up new distributions of stresses with altered restraints and
new patterns of buckling. There is a parallel with the formation of the
pattern over the wax glands in Calpodes. The coarser, first order pattern
is determined by the rate and position at which the cuticulin is deposited.
This limits future expansion resulting in the finer, second order pattern
of microtubercles. The interactions between stresses imposed by the
expanding cuticulin and restraints from the cells resulting in deformation and pattern formation, pose difficult problems which need detailed
study, but they may lead us closer to two basic problems: (1) the
mechanism by which the form of the cells is determined, and (2) the
means by which a pattern in time (determining, say the rate of cuticulin
or fiber synthesis) is translated to a pattern in space (the presence or
absence of fibers or cuticulin at particular positions on the surface of
the cell).
2. The Structure, Formation, and Growth of the Cuticulin Layer
The role of the cuticulin in the origin of surface patterns makes its
formation and growth of considerable interest. Also, there are several
parallels in structure between cuticulin and plasma membranes, and
the origin of cuticulin may be useful as a model for the origin of other
kinds of membrane.
a. The Structure of the Cuticulin. An early study upon Rhodnius resolved the tracheole lining as a double layer about 85 Â thick shortly
after its formation (Locke, 1958a). This double layer was also seen in
the cuticulin of developing scales in Ephestia (Paweletz and Schlote,
1964). Higher resolution and new methods of fixation (Locke, 1966a)
show that in Calpodes, the cuticulin is a triple layer at the time of its
formation, i.e., there are three dense laminae 1, 2, 3 (Figs. 17-19). The
central layer (2) is fainter than the two outer ones. The approximate
dimensions are given in Fig. 17A.
The cuticulin only remains as this symmetrical triple layer while it
is forming. After it completely covers the surface, or a little earlier, two
other types of change take place, the formation of micropores and the
separation of the outermost layer to become what may be the surface
layer of wax. At the time the molting fluid is being resorbed and in
some parts of fully formed tracheoles, the cuticulin is made up of dense,
rodlike, or cylindrical masses 25-30 Â in diameter, arranged normal to
the surface and separated from one another by spaces about 30 Â wide,
giving it a porous appearance (Fig. 20). A diagram of the structure is
MICHAEL LOCKE
remaining expansion in the axis can only be relieved by the formation
of fine transverse folds.
We can think of hierarchies of stresses, restraints, and deformation
which set up new distributions of stresses with altered restraints and
new patterns of buckling. There is a parallel with the formation of the
pattern over the wax glands in Calpodes. The coarser, first order pattern
is determined by the rate and position at which the cuticulin is deposited.
This limits future expansion resulting in the finer, second order pattern
of microtubercles. The interactions between stresses imposed by the
expanding cuticulin and restraints from the cells resulting in deformation and pattern formation, pose difficult problems which need detailed
study, but they may lead us closer to two basic problems: (1) the
mechanism by which the form of the cells is determined, and (2) the
means by which a pattern in time (determining, say the rate of cuticulin
or fiber synthesis) is translated to a pattern in space (the presence or
absence of fibers or cuticulin at particular positions on the surface of
the cell).
2. The Structure, Formation, and Growth of the Cuticulin Layer
The role of the cuticulin in the origin of surface patterns makes its
formation and growth of considerable interest. Also, there are several
parallels in structure between cuticulin and plasma membranes, and
the origin of cuticulin may be useful as a model for the origin of other
kinds of membrane.
a. The Structure of the Cuticulin. An early study upon Rhodnius resolved the tracheole lining as a double layer about 85 Â thick shortly
after its formation (Locke, 1958a). This double layer was also seen in
the cuticulin of developing scales in Ephestia (Paweletz and Schlote,
1964). Higher resolution and new methods of fixation (Locke, 1966a)
show that in Calpodes, the cuticulin is a triple layer at the time of its
formation, i.e., there are three dense laminae 1, 2, 3 (Figs. 17-19). The
central layer (2) is fainter than the two outer ones. The approximate
dimensions are given in Fig. 17A.
The cuticulin only remains as this symmetrical triple layer while it
is forming. After it completely covers the surface, or a little earlier, two
other types of change take place, the formation of micropores and the
separation of the outermost layer to become what may be the surface
layer of wax. At the time the molting fluid is being resorbed and in
some parts of fully formed tracheoles, the cuticulin is made up of dense,
rodlike, or cylindrical masses 25-30 Â in diameter, arranged normal to
the surface and separated from one another by spaces about 30 Â wide,
giving it a porous appearance (Fig. 20). A diagram of the structure is