SEXUAL PHASES IN TERRESTRIAL NEMERTEANS

¹ From the Osborn Zoölogical Laboratory, Yale University, and the Scripps Institution of Oceanography, University of California)

1. A series of 21 specimens of a species of terrestrial nemertean, Geonemertes palaensis, from tropical Pacific islands includes successive stages in the development of the gonads which show that this species is normally protandric and irregularly hermaphroditic, as previously described for G. agricola.

2. The primary male phase of the young individual is followed by a female phase which, however, may become functionally hermaphroditic in some individuals before the ova are fully ripe by the precocious development of some of the spermaries of the normally succeeding male phase. Opportunity is there by offered for self-fertilization.

3. The extent to which the female phase toward its close is accompained by the development of spermaries is highly variable, some individuals having in this phase only a few small spermaries and others many larger ones.

4. This sequence of alternating male and female (or hermaphroditic) sexual phases presumably continues throughout the lifetime of the individual.

5. Geonemertes palaensis is oviparous, while the terrestrial nemertean of Bermuda (G. agricola) is viviparous. The sexual phases, however, are similar in both species.

6. No direct evidence is available as to whether the great variability in the relative proportions of male and female gonads in different individuals following the initial male phase in both these species is due to physiological conditions imposed by environmental influences or to slight differences in the hereditary sexual endowment. Presumably both these factors may be associated.