THE SEXUAL CYCLE OF THE SHIPWORM, TEREDO NAVALIS

Abstract

The instability of the sexes of this mollusk is further explained and descr. by extending former studies to include the development and sexual differentiation of the young animals. The study included several features of development but emphasis was placed upon 2 chief points: i) Individuals functioning actively as [male][male]may rapldly change to [female][female]and shed abundant eggs. This all takes place during one and the same breeding season. Since this sex inversion takes place both in young animals of the current breeding season and in over-wintering adult animals it must be regarded as an essential part of the sexual cycle of this species. ii) During sex differentiation, [male][male]and [female][female]appear simultaneously. The gonads of the young are not exclusively [male]as required by the conception of the sexual cycle as protandric. Apparently sex is not rigidly fixed and there may be inversion of the sexes from [male]to [female]or from [female]to [male]at any time during the breeding season. The mechanism of the inheritance of sex is not apparent. This is not a protandric sexual cycle but an unstable one, in which slight external or internal changes may cause change of sex in either direction.