In 1949 while studying live chaetognaths, I often touched them with a bristle and observed that although they were very sensitive to touch on the body surface, the so-called tactile tufts or tangoreceptors were insensitive to gentle rubbing, to strong, rapid stroking and to jabbing. Since then I have had several opportunities to repeat this simple experiment and have tested seven or eight species including Eukrohnia hamata. In all cases the results were the same, no response from touching the

more »

... actile" tufts, immediate response from touching the tail fin or the body surface. On October 24, 1965 at eleven a.m., while swimming in shallow water in Tanabe Bay, I saw several species of Chaetognatha including Flaccisagitta enjlata, Parasagitta robusta, and Serratosagitta pacifica. One short stout individual with large seminal vesicles looked like Pterosagitta draco. I was able to catch it in a plastic bottle and in the laboratory confirmed the field identification of the still living, perfect specimen. I took this opportunity to repeat my earlier observations on its especially long "wings". When the tufts were bent back and forth with a needle, the arrowworm didn't show the slightest response. However, the gentlest touch to the tail fin evoked a powerful swimming reaction. Other parts of the body such as the trunk and head were somewhat less sensitive to touch than the tail, as in the other species tested earlier. It seems clear that the hairlike bundles or tufts as well as the "wings" are not tactile sensory structures. Apparently GEGENBAUR (1856) first suggested they were tactile after study of their structure. BuRFIELD (1927) called them tactile organs and this has since been repeated many times in the literature-see HYMAN (1959, p. 22) for example.