Editing Animal sexual behaviour (section)

===Flatworm===
[[Penis fencing]] is a mating behaviour engaged in by certain species of [[flatworm]], such as Pseudobiceros hancockanus. Species which engage in the practice are hermaphroditic, possessing both eggs and sperm-producing testes.<ref>{{cite web |url=http://www.pbs.org/kcet/shapeoflife/episodes/hunt_explo2.html |title=Fighting to mate: flatworm penis fencing |author=Leslie Newman |publisher=[[Public Broadcasting Service|PBS]]}}</ref>

Child-bearing, while necessary for the continuation of a species, requires considerable resources from the mother. Thus, from a biological point of view, it is preferable to be the father rather than the mother.

The species "fence" using two-headed dagger-like penises which are pointed, and white in color. The "winner" is the organism that inseminates the other. The sperm is absorbed through pores in the skin, causing fertilization in the "loser".