ABSTRACT
When globiferous pedicellariae of the echinoid Sphaerechinus granulans emit their venom, their head autotomizes and their stalk which remains on the test is submitted to resorption processes. Sectioning of the pedicellaria stalk also results in the resorption of this. On the contrary, fracture of the skeletal element which supports the stalk (the rod), without disruption of the non-calcified tissues, induces on both broken parts of this rod the development of stereom processes which will fuse together and reduce the fracture. No resorption phenomenon is apparent in these stalks. These results indicate that autotomy processes are not crucial to induce the resorption phenomenon. They also emphasize that the pedicellaria stalk, although ultrastructurally similar to the spine and showing stereom growth abilities, does not regenerate when sectioned as the spine does. We suggest that the intradermal ectoneural nerves ensheathed by inactive phagocytes which are characteristic of the pedicellaria stalk are involved in the triggering of the resorption processes.
