. Electro-physiology. Electrophysiology. 36 ELECTRO-PHYSIOLOGY CHAP. " sheath of Schwann," but is rather comparable with the con- nective tissue (" endoperiueurium ") which, in vertebrates, unites the axis-cylinders, along with their special sheaths, into primitive bundles of fibres, or nerve-trunks. Only that fine, homogeneous, nucleated sheath which partially invests the peripheral axis- cylinders (medullated and non-medullated) of vertebrates and some invertebrates is to be termed the sheath of Schwann. In the muscular nerve of crayfish, the neural sheath, both in the la
. Electro-physiology. Electrophysiology. 36 ELECTRO-PHYSIOLOGY CHAP. " sheath of Schwann," but is rather comparable with the con- nective tissue (" endoperiueurium ") which, in vertebrates, unites the axis-cylinders, along with their special sheaths, into primitive bundles of fibres, or nerve-trunks. Only that fine, homogeneous, nucleated sheath which partially invests the peripheral axis- cylinders (medullated and non-medullated) of vertebrates and some invertebrates is to be termed the sheath of Schwann. In the muscular nerve of crayfish, the neural sheath, both in the larger trunks and in parts where the axis-cylinders run singly, exhibits, even in the fresh state, and still more after treatment with the gold method, an obvious stratification, resembling in places the highly developed and richly nucleated connective- tissue sheath on the capsule of the Pacinian corpuscle (Fig. 150). A similar concentric layering appears in the neural sheath of several Orthoptera (locusts). In other cases, on the contrary ( many. FIG. 150.—Isolated muscular nerve from the abductor muscle of crayfish. (Gold and formic acid.) insects), the substance in which the axis-cylinder is embedded is finely granulated, like protoplasm (3). These relations between the nerve-fibres (axis-cylinders) of invertebrates and their sheaths only appear fully on staining the former by proper methods. The gold method, which was so much employed, after Cohnheim, has been superseded by the methylene- blue method of Ehrlich, more particularly for invertebrate animals. Biedermann has failed to determine a special and individual sheath within the common integument of the finer axis-cylinders of in- vertebrate nerves, unless the compacter layers of connective tissue immediately surrounding each axis-cylinder in the muscular nerve- trunk of the crayfish be recognised as such. As a rule, invertebrate nerves present a naked axis-cylinder within a common sheath, or substratum of connectiv
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