2. CHITIN AND MUCOSUBSTANCES
101
scopically visible fibers ("Balken"). This view receives substantial support from direct electron and ultraviolet microscopic examinations.
It is believed that, the optical axis being aligned with the micellar
axis, the micelles are in many cases of cuticular chitin, arranged in part,
parallel to the surface. Higher degrees of orientation are reported in
setae (60, 61) and in muscle tendons (62).
1. Orientation of Chitin Fibers
The visible laminated structure of anthropod cuticle appears to arise
from alternating layers of greater and less density rather than from different chemical constituents (63), the layers varying (64) in thickness
between 0.2 μ and 10 μ. In Schistocerca gregaria Forskäl, the rubberlike
ligaments of the prealar arm has a lamellar structure in which chitin is
reported to be interconnected with resilin. Similar regions were reported
(65) in the main hinge of the forewings. The chitin deposition in this
rubberlike cuticle, in which pore canals are absent, is quantal in nature,
each postimaginal lamella arising from the secretion of a constant
amount of chitin. In these locust tissues, the frequency of lamella formation declines with age. In Saroophaga, the outer zone of the procuticle
increases in thickness and laminates after separation from epithelium
(epidermis) by new endocuticle. The formation of lamellae does not
appear to be dependent on immediate contact with cells, or alternatively
their formation involves diffusion and deposition processes. The extracellular formation of laminated structures has been found also by
Picken et al. (45).
Most work, however, has been carried out on micelles and microfibers, using thin membranes. These have been found particularly suitable for direct electron microscopic examination. The value of 100 A. for
microfibers, it has been suggested (66), represents an average size of
crystallite that can fit across the main longitudinal axis of microfibers.
In thin lamellae from Donacia, chitin chains appear to be oriented
in the plane of the lamella, in a mosaic-like arrangement of differing
extents of crystallinity. The common forms of orientation in this cocoon
were at 90 degrees and at 45 degrees to its long axis.
The role of proteins and other agents forming complexes with polyN-acetylglucosamine is of considerable importance in relation to the formation of lamellae. In Hypoderma, microfibers are reported (55) to decrease in diameter on being treated under such conditions as to remove
protein, and there is growing evidence for the existence of such interaction products.
Consideration must be given to the view that orientation of chitin
crystallites may be influenced by the molding forces operating in the
101
scopically visible fibers ("Balken"). This view receives substantial support from direct electron and ultraviolet microscopic examinations.
It is believed that, the optical axis being aligned with the micellar
axis, the micelles are in many cases of cuticular chitin, arranged in part,
parallel to the surface. Higher degrees of orientation are reported in
setae (60, 61) and in muscle tendons (62).
1. Orientation of Chitin Fibers
The visible laminated structure of anthropod cuticle appears to arise
from alternating layers of greater and less density rather than from different chemical constituents (63), the layers varying (64) in thickness
between 0.2 μ and 10 μ. In Schistocerca gregaria Forskäl, the rubberlike
ligaments of the prealar arm has a lamellar structure in which chitin is
reported to be interconnected with resilin. Similar regions were reported
(65) in the main hinge of the forewings. The chitin deposition in this
rubberlike cuticle, in which pore canals are absent, is quantal in nature,
each postimaginal lamella arising from the secretion of a constant
amount of chitin. In these locust tissues, the frequency of lamella formation declines with age. In Saroophaga, the outer zone of the procuticle
increases in thickness and laminates after separation from epithelium
(epidermis) by new endocuticle. The formation of lamellae does not
appear to be dependent on immediate contact with cells, or alternatively
their formation involves diffusion and deposition processes. The extracellular formation of laminated structures has been found also by
Picken et al. (45).
Most work, however, has been carried out on micelles and microfibers, using thin membranes. These have been found particularly suitable for direct electron microscopic examination. The value of 100 A. for
microfibers, it has been suggested (66), represents an average size of
crystallite that can fit across the main longitudinal axis of microfibers.
In thin lamellae from Donacia, chitin chains appear to be oriented
in the plane of the lamella, in a mosaic-like arrangement of differing
extents of crystallinity. The common forms of orientation in this cocoon
were at 90 degrees and at 45 degrees to its long axis.
The role of proteins and other agents forming complexes with polyN-acetylglucosamine is of considerable importance in relation to the formation of lamellae. In Hypoderma, microfibers are reported (55) to decrease in diameter on being treated under such conditions as to remove
protein, and there is growing evidence for the existence of such interaction products.
Consideration must be given to the view that orientation of chitin
crystallites may be influenced by the molding forces operating in the