Copulation and Fertilisation in Hermaphrodites
Copulation between hermaphrodites is common. Flatworms possess a cirrus and penis that is inserted into the uterine vaginal opening of another worm. After copulation, the sperms are stored in a seminal receptacle. In earthworms, the genital papillae assist in mating, the sperms released from the male genital pore of one earthworm are received and stored in seminal receptacles (spermathecae) of another earthworm. Sperm transfer is thus mutual. Similarly cross fertilisation is possibly the rule in tapeworms when there are adjacent individuals inside the hosts gut, but self fertilisation among two different proglottids of the same tapeworm is as well known to occur. Majority of hermaphrodites tend to be protandrous that is male gonads maturing first, and this is a condition to ensure cross fertilisation. In protandrous hermaphrodites the gonads (testes and ovaries) may be separate organs and they mature at dissimilar times. In some rare cases as in certain gastropod molluscs there is a single gonad called ovotestis that produces both eggs and sperms. But the gonad first produces sperms and later the egg.