ABSTRACT
INTRODUCTION Species that possess sex organs employ a wide range of reproductive strategies. There are differences in the elicitation of the endocrine trigger for ovulation, in internal or external oocyte fertilization, in the number of viable offspring at birth, and whether there occur live births or births from hatched eggs. However, the initial development of the reproductive system shows a remarkable degree of homology across species, with phenotypic differences emerging from a rudimentary urogenital system that is essentially indistinguishable between males and females. This bipotential nature of inter-and intraspecies gonadal organ development was touched on over 75 years ago by the biologist Frank Lillie (1), who stated that, “There is no such biological entity as sex. What exists in nature is a dimorphism within species into male and female individuals . . ..”
