Earwigs (Insecta, Dermaptera) show astonishing diversity in penis morphology. In several families, males have a single penis (termed virga), whereas males of other families possess two functional virgae. Taxonomists have assumed that the two-virgae state is ancestral; however, ecological reasons why the ancestor acquired two virgae have not been explored. This study investigated in detail male and female genital structures, mating behaviour and insemination processes in the earwig Diplatys flavicollis (Diplatyidae). Diplatyidae are considered to be the most primitive family of earwigs. SEM and light-microscopy revealed that males of this species have two gonopores on each of two virgae, similar to those reported in other diplatyids (i.e. two double-barrelled penises), while females have four to six independent sperm-storage organs (spermathecae). Rapid fixation of mating pairs and insemination success of males from which one virga had been removed clearly revealed that only one virga was used for mating and was usually sufficient for inseminating multiple spermathecae. This finding rejects the one-to-one correspondence between male gonopores and female spermathecae. Based on allometric analysis of spermathecal variation, the possible significance of multiple spermathecae in relation to sperm-storage strategies of females is discussed. Compared to studies of male genital morphology, few studies have described spermathecal morphology. Based on compiled data of spermathecal and virgal morphology among earwigs, a parallel evolutionary trend between spermathecae and virgae from complicated (multiple) to simple (single) ones is suggested, and further investigation of the phylogeny, female genital morphology and insemination processes among earwigs is encouraged.

The functioning of female genitalia in many arthropods, especially the site and mode of sperm storage, may have a strong impact on the pattern of sperm usage, leading to differential male fertilization success and even varying offspring sex ratios. The female genital morphology of the linyphiid spider Pityohyphantes phrygianus was investigated, as this species was shown to possess an intriguing mechanism of sex ratio determination, possibly related to genital morphology. By means of SEM and serial semi-thin sectioning, two distinctly different spermathecae plus an additional sperm sac, equipped with several valves, were found on each side of the genital apparatus. Sperm is stored under different conditions, as one of the spermathecae exhibits large gland cells of different types that discharge their products into the spermatheca through long secretory ducts, whereas the other spermatheca is surrounded by a simpler type of gland cell. Furthermore, there are folds instead of closed ducts leading to the spermathecae, and from the spermathecae to the oviduct. The latter fertilization-fold runs inside the copulatory chamber and enters the oviduct from the outside. The mechanisms for sex ratio bias in spiders are discussed. The occurrence of two types of spermatheca of which one is twisted, provides good evidence for the involvement of female genital morphology in sex ratio control of P. phrygianus offspring. Data are compiled on species for which information is available on sex ratio and female genital morphology. We put forward a hypothesis that in species with a skewed sex ratio, there is interaction between female genital morphology and behaviour, i.e. change of body position before, during or immediately after sperm transfer.

In a recent paper Raxworthy & Nussbaum (1995) included the Madagascan dwarf chameleons Brookesia peyrierasiand B. tuberculata in the synonymy of B. minima, regarding known hemipenial differences between B. tuberculata and B. peyrierasi as artefacts. Our studies demonstrate that the hemipenis description of B. tuberculata by Brygoo & Domergue (1975) was largely correct and referred to unusual but real structures. The enormous differences in the hemipenis morphology of B. tuberculata (hemipenes of six specimens examined) and B. peyrierasi (hemipenes of five specimens examined) strongly suggest that they are not conspecific. Furthermore, morphological differences in the arrangement of head crests and expression of supraocular spines were noted between these two taxa and B. minima. The differentiation of the three taxa is furthermore corroborated by both univariate and multivariate analyses of morphometric data. We therefore propose to consider Brookesia minima, B. peyrierasi, and B. tuberculata as distinct species. This conclusion corroborates the validity of biogeographic regions as suggested from the analysis of distribution patterns of other Brookesia species.