Fine structure of peripheral terminations in the porous sensillar cone of larvae of Ctenicera destructor (Brown) (Coleoptera, Elateridae), and probable fixation artifacts
Nodes occur naturally on the dendritic branches in the receptor-lymph cavity of the antennal sensory cone in larvae of Ctenicera destructor. They increase in number, are often greatly expanded, and may separate from the dendrites as fixation artifacts. Extracellular dictyosomes originate from terminal nodes of the dendritic branches. These dictyosomes secrete vesicles, believed to contain lipoidal substances, directly into the fluid in the receptor cavity. These vesicles either coalesce into large lipoidal globules which produce the peripheral sensory tubules that traverse pores in the covering cuticle, or themselves attach directly to the tubules. The sensory tubules are lipoidal in nature. It is suggested that they serve to conserve moisture in the sensillum and to channel stimulating molecules through the cuticle to the lymph in the receptor cavity. The dendrites are not attached directly to the sensory tubules, but are believed to gain contact with the stimulating molecules through the receptor lymph. The lipoidal substance for sensory tubule secretion is probably transported into the sensory cone by the neurotubules within the dendrites. The results from a technique using glutaraldehyde fixation, ammoniacal silver treatment, and lead staining, without osmium fixation, are described and discussed.