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The structure of the seminal receptacles and associated accessory pouches in the reproductive tracts of four species of Australian ovoviviparous peripatopsids is described to identify features that may relate to their inferred mode of insemination. Euperipatoides rowelli is a dermal inseminator whereas Phallocephale tallagandensis, Ruhbergia bifalcata and Cephalofovea clandestina, species with head structures in males, are considered to be vaginal inseminators. Contrary to our expectations, E. rowelli, R. bifalcata and C. clandestina have very similar seminal receptacles and display two types of accessory pouches: funnel accessory pouches that open to the haemocoel and spherical accessory pouches in which destruction of excess sperm occurs. On the other hand, Ph. tallagandensis differs in the form of its accessory pouches. Although these pouches have no direct opening into the haemocoel, sperm were observed in the act of directly penetrating their walls to gain entry from the haemocoel. Hence, despite differences in the form of their accessory pouches, all species display features that provide the potential for entry of sperm into the female reproductive tract from the haemocoel. This finding has caused us to reconsider our initial assumptions of vaginal and dermal insemination as mutually exclusive reproductive strategies. Indeed, we propose that species of peripatopsids with head structures in males that were considered to be obligate vaginal inseminators may in fact be facultative, with vaginal insemination of sexually immature females when their uterus is short and free of developing embryos followed by dermal insemination to maintain the level of sperm in storage in the seminal receptacles. This study has also provided morphological evidence for mechanisms that may facilitate female control of paternity. [ABSTRACT FROM AUTHOR]