ELECTRON MICROSCOPIC STUDY OF GIANT NERVE FIBER OF GIANT SQUID DOSIDICUS GIGAS

The present work deals with the ultrastructure of the giant nerve fiber of the giant squid Dosidicus gigas. The axons studied were 800-1200 μ in diameter. The axolemma (membrane of the axon proper) shows a three-laminated pattern alternated with zones made up of repeated globular units. Local thickenings attached to the axolemma internal leaflet are also observed. The axoplasm shows a peculiar structure formed by clusters of vesicles, 600-1000 Å in diameter, and clusters of granules of about 400 Å in diameter. Both components form elongated massive bodies along the axon. Two types of axonal mitochondria were observed: one type rounded, over 0.6 μ in diameter, found only near the axolemma; and the other, elongated, about 0.4 μ in width by 3 μ in length, scattered all over the axoplasm. The Schwann layer, 1.5-6 μ thick, formed by a single row of Schwann cells, is crossed by channels. These channels are more tortuous than in the tropical species. The Schwann layer is covered outside by the basal lamina made up by a thread-like dense material, intermingled with connective tissue fibrils. Following this zone is the orderly arranged endoneurium, formed by alternated layers of cells and fibrils. Some endoneurial cells bear pigment-like granules. Blood vessels are found alongside the endoneurium. © 1969 Academic Press, Inc.