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Abstract

During the courtship of Helix aspersa, the snails push calcareous darts into one another. To examine the importance f this unusual action for the normal expression of their sexual behaviour, one group of Helix aspersa was prevented from exchanging darts by surgically removing their dart sacs. Another group of Helix aspersa had their digitiform glands surgically removed. These glands secrete a mucus that coats the dart. Glandless snails were capable of exchanging darts, but the darts lacked their normal mucus coating. Both dartless and glandless pairs required more courtship time to reach copulation than did sham-operated controls. Therefore, it appears that it is the mucus from the digitiform gland, not the mechanical action of the dart, which affects courtship duration.

Injections of gland homogenate decreased the courtship duration of sexually receptive, dartless, and glandless snails. Gland homogenate also increased the size of the recipient's genital eversion, and retarded locomotion. The mucus was only effective if it entered the circulatory system of a sexually receptive snail at a specific stage of genital eversion.

The active agent in the digitiform gland mucus fulfills the requirements for the substance to be classified as a pheromone. It enters the circulatory system of the conspecific via inoculation by the dart.