External morphology of the developing hemipenes of the dwarf chameleon, Bradypodion pumilum (Reptilia: Chamaeleonidae)

The external morphology of the hemipenes of squamate reptiles is often complex and has been widely employed in systematic studies. Little is known, however, of the development of these patterns and thus of the potential polarity of the character states used in systematic studies. Analysis of three developmental stages of the hemipenes of the chameleon Bradypodion pumilum using scanning electron microscopy reveals that the complexity of pattern emerges gradually. Initially the hemipenial anlagen appear as simple, external lobes that develop in close association with the cloaca. By stage 38 a shallow sulcus spermaticus is evident and calices have begun to appear. By stage 41 embryos possess a deep, protected sulcus and two pairs of distal lobes. These lobes will eventually differentiate into semicircular disks (rotulae) with serrated margins that are characteristic of many members of the family. The complex external morphology of the hemipenes that is of significance in systematic studies and of assumed importance in copulatory mechanics may not be expressed until sexual maturity is reached.