A sex pheromone secreting gland in the terrestrial snail, Euhadra peliomphala

Abstract

The head-wart found in the snail, Euhadra peliomphala, consists of a number of elevated dermal tubercles covered by a particularly thick epithelium. The head-wart and its epithelial cells attain full size by rapid growth at the time of sexual maturation. When two snails meet in the breeding season, their head-warts become conspicuously protuded. After touching the partner's head-wart with large tentacles, each becomes excited, protrudes its penial mass, and finally copulates. Protrusion of the head-wart and copulation are observed at the same time. By the use of head-wart extract similar sexual behavior can be experimentally induced in snails. From these observations, it may be concluded that it is the epithelial surface of the head-wart of a sexually mature snail which releases the substance that promotes sexual behavior. This physiologically active substance is considered to be a kind of sex pheromone. This pheromone does not appear to serve as a sexual attractant but serves rather to sexually excite another snail thus evoking a courtship response following their initial encounter.Our knowledge of pheromones has been derived mainly from study of insects and particularly from study of their sex pheromones (Jacobson, '72). Research on pheromones of invertebrates other than insects is relatively non-existent. However, numerous papers have appeared recently on pheromones on organisms all the way from acellular organisms to nematodes, non-insectan arthropods, molluscs, and echinoderms. With the advance of this pheromone research, it is now clear that pheromone mediated behavior is ubiquitous throughout the animal kingdom (Birch, '74; Shorey, '76). In snails, pheromones have been In 1935 Taki reported an irregular polygonal tissue situated between the two optic tentacles on the head of many terrestrial snails. He named it "head-wart.'' The function of the head-wart has not been reported. Our paper deals with the clarification of the function of the head-wart. We suggest that the head-wart is a sex-pheromone-secreting gland. MATERIALS AND METHODSThe animal used in the experiments re- ported here was the terrestrial snail, Euhadra peliomphala. Snails were collected in field and were kept under natural conditions. In Euhadra peliomphala the main breeding season is in June and again in September under natural conditions.In order to make observations under a light microscope, the head-wart (or head-wart regions) was fixed in Bouin for 24 hours, dehydrated with butyl alcohol, embedded in paraffin wax, and sectioned at 5 pm. The serial sections were stained with Mayer's hematoxylin and eosin.To discover something of the function of the head-wart, extracts were applied to snails maintained in small glass containers, each 20 cm diameter x 5 cm high. Ten head-warts in a well-developed state were extracted with 70% ethyl alcohol. The extract was absorbed on to filter paper, dried, and then moistened with distilled water before being introduced into the floor of the container. In the two control groups, a 70% ethyl alcoh...

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