The genitalia of most male cockroaches are ornate, strongly asymmetrical, and differ, at times dramatically, among species. Because they are among the primary characters used in cockroach taxonomy, some beautifully detailed drawings are available, but we have little understanding as to the functional significance of most components. The genital sclerites are usually divided into the left, right, and median (also called ventral) phallomeres. These can be relatively simple and widely separated, or form groups of convoluted, well-muscled structures elaborately subdivided into movable rods, hooks, knobs, spines, lobes, brushes, flagellae, and other sclerotized processes (Fig. 6.11).
Several male genital sclerites are associated with the process of intromission and insemination; these include "tools" for holding the female, positioning her, and orienting her genitalia to best achieve spermatophore transfer. In Blatta orientalis, for example, all five lobes of the left phallomere, together with the ventral phallomere, serve to stabilize the ovipositor valves of the female, while a sclerite of the right phallomere spreads the valves from the center so that the spermatophore can be inserted (Bao and Robinson, 1990). Nonetheless, phallomeres are nearly absent in some blaberids, suggesting that elaborate hardware is not always a requisite for successful copulation.
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