In C. nigrescens and in some other species a zooid may contain a pair of ovaries, a pair of testes, or an ovary and a testis, although the males, females and hermaj phrodites do not differ from one another in external characters.
The testes during development become hollowed out and are prolonged into the vasa efferentia.
The ovary and testes are heaped-up masses of red or yellow cells due to a proliferation of the cells lining the coelom.
The former consist of one pair or more of vesicular testes communicating by fine ducts with a vesicula seminalis.
The testes reach forward to the fifth and even to the second segment, and open one each side of the anus.