The swim bladder with two anterior extensions extending forward to basioccipital on both sides above auditory capsule; two posterior extensions extending into haemal funnel beyond posterior end of body cavity (the roots of two posterior extensions are non-adjacent and two posterior extensions are not well-knitted); a single duct-like process originating from ventral surface of swim bladder (between the roots of two posterior extensions) and reaching urogenital opening.
A single duct-like process originating from ventral surface of swim bladder and reaching urogenital opening, the origin of the duct-like process is at the terminal of swim bladder and between the roots of two posterior extensions; a subextension of duct-like process is present, small but complex, connect with a sanguineous vesicle close to vertebra, with unknown function.
The shape of the urogenital opening
in males is round and generally larger in circumference than the anal opening, whereas females tend to have a V- or U-shaped opening that is smaller in circumference than the anal opening.
In rare cases, the eggs can be transmitted to the urogenital opening
, and the larvae then hatch into the urogenital region.
In a study conveyed by McComish (1968) in bluegills Lepomis macrochirus, the criterion of presence (in females) or absence (in males) of a large, swollen, scaleless area surrounding the urogenital opening has been used in sexual determination.
Jeffrey et al, 2011 used three parameters (the shape of the urogenital opening, the shape of the anterior edge of the urogenital opening when thumb pressure was applied to the abdomen and the presence or absence of swelling around the anus) in sexual identification of yellow perch Perca flavescens.
However, when the researchers presented male wallabies with swabs from the urogenital opening
of females, some on heat, others off, to see which they preferred, the results were inconclusive.
Urine was collected directly from the bat's urogenital opening
, before the blood sampling, with a cotton swab that was immediately placed in a cryotube containing 1 mL viral transport medium.