hermaphrodites
A Hermaphrodite has both male and female genetalia as well as an ovary and testies.
  Very few "true hermaphrodites" exist Only about 300 have been described over the past 200 years.  
Most hermaphrodites are just structural and are due to mistakes in the development of the male/femals genetalia.
 
True Hermaphrodites are probably due to a merging of two fertilized eggs, where one was a female and one was a male. It is the opposit of the production of twins.
 
chimera
Interesting animal biology
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