The externa remains immature until a male cypris injects its internal cells into a female's externa, where cypris cells transform into sperm-producing cells within a pair of cypris cell receptacles which were once called the testes.
The externa remains immature. A male cypris injects its internal cells into a female's externa. Cypris cells transform into sperm-producing cells within a pair of cypris cell receptacles. These producing cells within a pair of cypris cell receptacles were once called the testes.