Direct development explained

Direct development is a concept in biology. It refers to forms of growth to adulthood that do not involve metamorphosis. An animal undergoes direct development if the immature organism resembles a small adult rather than having a distinct larval form.^[1] A frog that hatches out of its egg as a small frog undergoes direct development. A frog that hatches out of its egg as a tadpole does not.

Direct development is the opposite of complete metamorphosis. An animal undergoes complete metamorphosis if it becomes a non-moving thing, for example a pupa in a cocoon, between its larval and adult stages.^[2]

Examples

• Most frogs in the genus Callulina hatch out of their eggs as froglets.
• Springtails and mayflies, called ametabolous insects, undergo direct development.^[3]

Notes and References

1. Direct development of the bush frog Raorchestes longchuanensis (Yang and Li 1978) under laborary conditions in Southern China. March 7, 2023. Journal of Natural History. 123–132. Fang Yan. Xiaolong Liu. Yinpeng Zhang. Zhiyong Yuan. May 28, 2021. 55 . 1–2 . 10.1080/00222933.2021.1895349. 236202923 .
2. Complete metamorphosis of insects. Jens Rolff. Paul R. Johnston. Stuart Reynolds. 10.1098/rstb.2019.0063. August 26, 2019. 31438816. 374. 1783. Philos Trans R Soc Lond B Biol Sci. 6711294 .
3. Book: March 19, 2023. Developmental Biology. 6. Scott F. Gilbert. Sunderland, MA . Sinauer Associates. 2000. Metamorphosis: The Hormonal Reactivation of Development.