Structure and function of the male copulatory apparatus of the nematodes Capillaria hepatica and Trichuris muris

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Abstract
The anatomy of the terminal male reproductive system was studied by light microscopy and by scanning and transmission electron microscopy. In C. hepatica a common muscle sphincter surrounds the vas deferens and intestine at their point of juncture. The cloaca is divisible into proximal and distal portions. The spicule is formed in a short ventral spicule pouch but lies mainly in the distal cloaca. The spicule is retracted in C. hepatica by a paired retractor muscle and in T. muris by a single retractor muscle. Protraction of the spicule occurs by contraction of longitudinal muscles surrounding the distal cloaca. This results in the surface layers of the cloacal cuticle being everted as the spicule sheath. The spicule is tubular with a cellular core including multiple sensory receptors at its tip. The spicule is probably solely a chemosensory organ. Mechanical stimulation in the region of the distal cloaca resulted in activation of the spicule and spicule sheath. Response to mechanical stimulus is age dependent.