To emerge from the egg case, Argiope aurantia spiderlings must penetrate a tightly woven outer cover composed primarily of large-diameter cylindrical gland fibers and small-diameter fibers, likely of aciniform gland origin. They accomplish this using enzymatic digestion and mastication to form a communal hole in the outer cover. The involvement of proteolytic enzymes in this process was demonstrated by zymography of spiderling homogenates and washes made from the edges of holes. The specific source(s) of the proteases is unknown, but histological examination of spiderling sections indicates that the digestive tract, venom glands, and gnathocoxal glands are all functioning at the time of emergence from the egg case. Observations on edges of holes indicate that spiderlings are able to solubilize the small-diameter fibers completely, but cylindrical gland fibers only partially. In the outer cover, cylindrical fibers are composed of numerous fibrils embedded within a matrix. Spiderlings appear to be unable to solubilize the fibrils, but digestion of the matrix allows the spiderlings to push the fibrils aside to create the opening.
Microanatomy of the anterior median eyes (AME) of a lycosid spider (Lycosa tarentula) shows two classes of photoreceptors in the retina: dorsal and median visual cells (A) are polygonal in crosssection and bear rhabdomeres on all their faces; ventral visual cells (B), rectangular in section, bear rhabdomeres only on two opposite faces; rhabdomes are aligned in parallel series and successive lines of rhabdoms are oriented orthogonally to each other. Receptor A cells are wider than Β cells, and about twice as numerous. In AME optic nerve, axons are also of two types, large and small, and the optic centre shows thick and narrow fibres, from the second order neurons, being separated by connective and glial cells. Anterior median eyes of second stage juveniles already present the same structure as those of adults. A similar anatomical structure was previously described in the AME of an agelenid spider by Schröer (1974). Since the detection and analysis of polarized light by agelenid and lycosid AME have also been demonstrated, it is suggested that the analysers of the e-vector of sky-polarized light are in the receptor Β cells and that the analysis is a successive process using a twisting of the retina due to the action of two muscles.
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