quality:correction, structural:scholar_edition
Reproduction

Caecilians are the only order of amphibians to use internal insemination exclusively (although most salamanders have internal fertilization and the tailed frog in the US uses a tail-like appendage for internal insemination in its fast-flowing water environment). The male caecilians have a long tube-like intromittent organ, the phallodeum, which is inserted into the cloaca of the female for two to three hours. About 25% of the species are oviparous (egg-laying); the eggs are laid in terrestrial nests rather than in water and are guarded by the female. For some species, the young caecilians are already metamorphosed when they hatch; others hatch as larvae. The larvae are not fully aquatic, but spend the daytime in the soil near the water.

About 75% of caecilians are viviparous, meaning they give birth to already-developed offspring. The foetus is fed inside the female with cells lining the oviduct, which they eat with special scraping teeth. Some larvae, such as those of Typhlonectes, are born with enormous external gills which are shed almost immediately.

The egg-laying herpelid species Boulengerula taitana feeds its young by developing an outer layer of skin, high in fat and other nutrients, which the young peel off with modified teeth. This allows them to grow by up to 10 times their own weight in a week. The skin is consumed every three days, the time it takes for a new layer to grow, and the young have only been observed to eat it at night. It was formerly thought that the juveniles subsisted only on a liquid secretion from their mothers. This form of parental care, known as maternal dermatophagy, has also been reported in two species in the family Siphonopidae: Siphonops annulatus and Microcaecilia dermatophaga. Siphonopids and herpelids are not closely related to each other, having diverged in the Cretaceous Period. The presence of maternal dermatophagy in both families suggest that it may be more widespread among caecilians than previously considered.

Herpele squalostoma caecilians vertically transmit the mother's microbiome to their offspring through maternal dermatophagy. In comparison to other amphibians, the extended parenting of caecilians can provide beneficial bacteria and fungi, but this transmission risks the spread of diseases like chytridiomycosis.