Usually herptiles that are kept properly will breed as a matter of course. To date few attempts have been made to breed Australian frogs in captivity. Gerry Marantelli and others at the Amphibian Research Centre in Melbourne, Victoria, have in the 1990's had some spectacular breeding successes of rare and little-known species of frogs.
Tortoises kept in captivity for a number of years produce eggs largely as a matter of course. Likewise for crocodilians.
Snakes and lizards however seem to be the hardest reptiles to breed in captivity. It is believed that both males and females have sexual cycles.
When their cycles coincide and mating takes place, breeding occurs.
If reptiles kept indoors experience no temperature variation during the year, they often fail to breed. Some cooling is required to initiate spermatogenesis in males, and ovulation in females. Most breeders 'cool' their snakes and lizards for 6 to 12 weeks prior to anticipated breeding's.
In some species, breeding cycles occur up to 9 months after the initial cooling, meaning that production of offspring may take up to 18 months from a given 'cooling' period.
'Cooling' involves the dropping the temperature of the reptile so that it is too cold to feed, and it goes into a relatively inactive state. (No reptile should be cooled to a point where it may be harmed. 15-20 degrees celcius is usually sufficient to initiate breeding activity).
To initiate mating, separation of the sexes is usually advised. When isolated males cease feeding and 'pace' their cages, they are usually interested in mating. By placing them with a receptive female at this time, successful copulation will usually occur. As reptiles are most sexually active during periods of falling air pressure, often associated with 'fronts', these are the periods that separated sexes should be re-introduced to each other.
Some reptile breeders vary photo-period (daylight hours) in a bid to initiate breeding activity.
Gravid (pregnant) reptiles must be treated with extreme care, as the wrong set of temperature or other conditions, can lead to death of unlaid eggs or unborn young. Gravid reptiles that are kept too warm or cool, will abort. (The term gravid is used to when eggs or young are in the oviducts. This is the normal situation in reptiles, but only occurs in mammals during birth).
To continue to the rest of this section (Incubating Reptile Eggs)
The above was from the book Australian Reptiles and Frogs by Raymond Hoser and now available on a fantastic CD-Rom along with a vast amount of other information, papers and the like on reptiles, frogs and other wildlife.