Although the Bidder’s organ in male bufonids has been reported since the last century (Spengel, 1876), available information about its morphology is still scarce. The Bidder’s organ is specific for the Bufonidae and has been cited as a rudimentary ovary-like structure in males of the specimens (Vitale-Calpe, 1969; Pancak-Roessler and Norris, 1991; Duellman and Trueb, 1994). We previously pointed out that the Bidder’s organ of male Bufo ictericus has a structural apparatus able to produce sexual cells. The Bidder’s organ is made up of a cortex and a medulla. The cortical region shows an ovarian morphology, exhibiting follicles in different stages of development. A small medullar region contains some fairly large blood vessels, notably coiled arteries and convoluted veins. Melanin pigment cells are also detected in the medullar region (Farias et al., 2002).
In this study, female Bidderian follicles are similar to ovarian follicles; they show the basic structure, in which a single continuous layer of follicular cells surrounds the oocyte. Tanimura and Iwasawa (1992), who studied the ovary and male Bidder’s organ in young toads of Bufo japonicus formosus, showed similarities between ovarian follicles and male bidderian follicles. Female Bidder’s organs have the same morphological characteristics as observed in male Bidder’s organs described by Farias et al. (2002).
Duellman and Trueb (1994) commented that the Bidder’s organ occurs only in male bufonids, and is used as a systematic characteristic. However, in this study, we prove that the female of Bufo ictericus may also have a typical Bidder’s organ in close spatial relationship with ovary.
In Bufo ictericus, the Bidder’s organ of females exhibits the usual morphological characteristics as previously described by us for males. This data suggests that the Bidder’s organ is not a structure exclusive to male bufonids, but it may also occur in active females. It is still unclear if these females originate from active males or if the Bidder’s organ represents an embryonic remnant.