Summary
The external and internal fine structure of the housefly interfacetal hair and its sensory dendrite was studied with the scanning and transmission (high and low voltage) electron microscopes. The hair shaft contains no dendrites, and is usually situated within a socket on the lens surface. Immediately beneath and directly connected to the base of each hair is a bipolar neuron whose dendrite tip is enveloped in a sheath cell which, in turn, is surrounded by a second sheath cell. Septate junctions are seen between all these cells and contiguous portions of a large pigment cell. At the hair base, the dendrite of the neuron terminates in a tubular body only 1.5 μm in diameter which is filled with about 400 microtubules in highly ordered (in parallel pentagonal and hexagonal) arrays and whose sides are fused to neurofilaments in parallel. Another filament (ca. 70 Å diameter) is in the center of each microtubule-neurofilament polygon. Structures proximal to the tubular body are typical for a scolopoid sensillum, i.e., connecting cilium (9×2+0 microtubules) with rootlet and basal bodies, unmodified dendrite, perikaryon and axon. The axon has not been traced to its synapse. The high degree of internal organization and shortness of the tubular body, as well as its eccentric insertion into the hair shaft lead to the hypothesis that this hair may be a highly sensitive mechanoreceptor. On the basis of their single innervation, these hairs could monitor flight speed from the degree of hair deflection caused by wind in general or particular laminar air currents flowing past the eyes during flight.
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We are especially grateful for support from the University of Wisconsin Graduate School, Project 160392 and the College of Agricultural and Life Sciences, Hatch Project No. 1916. Mr. Gary Gaard and Mr. Martin Garment helped in TEM and SEM-darkroom procedures, respectively. For assistance with the HVEM we heartily thank the following members of the Department of Zoology: Professor Hans Ris for his consent to the project, Associate Professor Dale E. Johnson, Physicist in charge, and Dr. Damian S. Neuberger, Specialist. We are most appreciative of a critical reading of this manuscript by Professor R.W. Guillery, Department of Anatomy.
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Chi, C., Carlson, S.D. The housefly interfacetal hair. Cell Tissue Res. 166, 353–363 (1976). https://doi.org/10.1007/BF00220131
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DOI: https://doi.org/10.1007/BF00220131