The gonads ( sexual organs ) of both male and female turtles are paired.
The female ovaries are quite large and occupy a substantial part of the turtle's viscera. The male penis in its relaxed state is completely contained within the cloaca. When sexually excited the penis extends to its full length through the vent, and curves downward and slightly forward.
The size of the male and females is about the same in most turtles . However, in some species males might grow much larger in some species, like the alligator snapping turtle or the giant tortoises, while in certain other types of turtles females are much larger than males ( for example Graptemys barbouri in which the female - about a foot in length - is about 4 to 5 times larger than the male ).
The tail of male turtle is usually longer and thicker than the tail of female turtle.
After various courtship rituals ( differing according to species ), the male turtle climbs the female from the back and secures itself on top of her by grabbing the edges of the carapace with his claws ( which are exceptionally long in some species ).
The copulation of aquatic turtles takes place in water. After a period of time eggs are laid in a nest dug in the soil ( usually a moist soil ).
All turtles reproduce by means of eggs, and some female turtles can produce fertile eggs even several years after the last possible contact with a male.
After a period of incubation the eggs hatch. The male - female ratio of the hatchlings depands on the surrounding temperature during incubation. Temperatures around 25 C produce males, and temperatures of either 20 or 30 C produce females.