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Quarterly Journal of Microscopical Science, Vol s3-104, 551-559, Copyright © 1963 by Company of Biologists

Muscle Fibres and Efferent Nerves in a Crustacean Receptor Muscle

MELVIN J. COHEN 1

1 Department of Biology, University of Oregon, Eugene, Oregon, U.S.A.

The accessory flexor muscle of the crab myochordotonal organ consists of two kinds of muscle-fibres. In one type the fibrillar material has a uniform punctate appearance in cross-section. The Z bands are often broken across the fibre width and are spaced 2 to 3µ apart. These resemble the ‘Fibrillenstruktur’ muscle of vertebrates. In the second fibre type the fibrillar material appears as large clumps in cross-section and it is often difficult to distinguish the outlines of individual fibres. The sarcomere length is 10 to 12µ. These resemble the ‘Felderstruktur’ muscle of vertebrates.

Two types of expanded structures are seen in conjunction with the two efferent neurones innervating this muscle. With fresh material under phase microscopy one type appears as a 20 by 40µ rectangular plaque containing vacuoles as well as dark clumps and granules. The other kind of enlargement consists of a group of spheres giving the appearance of a grape cluster and measuring 40 µ in its greatest dimension. It is suggested that these expanded structures may be associated with efferent nerve terminations in this muscle.






© The Company of Biologists Ltd 1963