The phylogenetic distribution and morphological variation of the ‘pouch’ in female snakes


Dustin S. Siegel, Department of Biology, Saint Louis University, 3507 Laclede Avenue, St. Louis, Missouri 63103, USA. E-mail:


Siegel D.S., Miralles A, Trauth S.E. and Aldridge R.D. 2011. The phylogenetic distribution and morphological variation of the ‘pouch’ in female snakes. —Acta Zoologica (Stockholm) 93: 400–408.

The urodaeum of female snakes is a chamber that receives the oviducts, urinary ducts, and intestine. Previous studies have indicated that a derived region of unknown function persists between the urodaeum and oviducts in some snakes of the Colubroides. This structure was recently termed the ‘pouch’; however, it is also commonly referred to as the vaginal pouch. A broad sampling of female snakes revealed that the pouch evolved once on the branch leading to Colubroides. The presence of the pouch in Colubroides is not unambiguous, as this feature was lost in some members of the Atractaspididae and Lamprophiidae. Variation was also observed in pouch morphology between taxa of the Colubroides. Variation included the following: (1) whether the pouch was bifurcated and if so, were the arms of the pouch separated caudally, (2) whether separated pouch arms were split by a caudal bifurcation of the urodaeum or through medial septa of the pouch arms, and (3) the absence or presence of oviducal papillae invading the cranial/lateral extremity of the pouch. The variation in pouch morphology observed does not appear to be correlated with the evolutionary history of Colubroides and polymorphism within families is common.