organs in animals that serve in males to introduce sperm into the body of the female, and in females to receive the copulative organ of the male and often to store the sperm in viable condition for a more or less prolonged period. There are male and female copulative organs.
Copulative organs are found only in animals with internal fertilization: many worms, mollusks, and arthropods; some fish and apodal amphibians; almost all reptiles, except the tuatara; some birds; and all mammals. True copulative organs are usually formed from the terminal sections of the sex ducts. There are copulative organs that are not anatomically connected with the genital system and that function sexually only incidentally. True copulative organs are found in Ciliata, flukes, tapeworms, and representatives of the higher groups of arthropods; among vertebrates, reptiles, birds, and mammals have them.
The function of copulative organs in males may be performed by extremities (in crustaceans and arachnids), appendages of fins (in fish), mouth organs (in ticks, solpugids, and apterous insects), and antennae (in some cephalopod mollusks like hectocotylus). Usually the sperm is introduced by the copulative organ into the genital opening of the female, and more rarely, under the skin by piercing the wall of her body (some Ciliata, parasitic myzostomes, and certain leeches and rotifers). The morphological characteristics of the copulative organs are often important taxonomic signs.