A Substance Inducing the Loss of Premature Embryos From Ovigerous Crabs

The embryos of an estuarine terrestrial crab (akate-gani; Sesarma haematocheir) are attached by a funiculus to ovigerous hairs on the maternal pleopods, and are ventilated by the female until hatching occurs. When females were kept in a small quantity of diluted seawater (about 10%), hatching and larval release occurred in all cases. In contrast, when the medium was hatch water (i.e., the filtered medium into which larvae had been released), most ovigerous females liberated their embryos prematurely, but hatching did not occur. The egg masses (cluster of embryos) carried by these females were not released as usual, but were gradually extruded from the brooding chamber, and within a few days all had dropped to the bottom of the beaker. No morphological changes were found on the outer egg membrane, the funiculus, or the coat investing the ovigerous hairs of females kept in hatch water. But the ovigerous hairs did slip easily out of the coat, and this caused the extrusion of the egg masses. The active factor--called incubation disrupting substance--was stable with freezing, but heat-labile. In normal females (i.e., those not treated with hatch water), broken egg cases and funiculi remain for a time after hatching with the coat on the ovigerous hairs, but they are gone by the morning after hatching. So the secretion of this incubation-disrupting substance may participate in cleaning the ovigerous hairs of old investing coats and funiculi after larval release, thus preparing for the attachment of the next clutch of embryos. In addition, this substance may play a role in hatching.