In annelids like Nereis, earthworm, leech, etc, the tubular coiled structures called nephridia are excretory organs. In phylum-Arthropoda, insects, centipedes, millipedes and arachnids possess Malpighian tubules as their principal excretory organ. Analogous organs have almost similar appearance and perform the same function but develop in totally different groups and are totally different in their basic structure and developmental origin, eg, wings of butterfly, birds, bats. The homologous organs have common origin, perform varied functions and have different appearance, eg, thorns of Bougainvillea and tendrils of Cucurbita. Vestigial organs are useless remnants, which might have been large and functional in the ancestors, eg, nictitating membrane, vermiform appendix, etc.