Feeding Responses To Sucrose in the Pond Snail Lymnaea Stagnalis After Nerve Section and Tentacle Amputation

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Abstract
Many observations on the behaviour of aquatic gastropods have revealed the vital importance of chemoreception in the life of these animals. It plays a role in a great variety of activities such as mating, prey recognition, predator avoidance and feeding (for references see KOHN, 1961). However, our knowledge concerning the biological basis of these activities is definitely incomplete. Research on the structure and function of chemosensory elements is indeed difficult since various levels of organization (behavioural, morphological, physiological) are involved. Moreover, experimentation using methods such as destruc- tion of receptors or interruption of connections with the central nervous system is complicated due to the (anatomically) diffuse organization of the relevant sensory systems. Chemoreceptors do not occur exclu- sively in discrete sense organs. Observations on responses to food in lymnaeid snails showed that chemosensitivity is present over the whole skin, particularly at the frontal part of the body (PIERON, 1908; BOVBJERG, 1968). Recent ultrastructural studies (ZYLSTRA, 1972) on epidermal sensory cells in freshwater pulmonates (Lymnaea stagnalis, Biomphalaria ?fe?eri) re- vealed the presence of cells whose morphological characteristics indi- cate a chemoreceptive function. The present paper concerns the detection of chemosensitive areas and their associated nerves in Lymnaea stagnalis. The approach involves a stimulus-response relationship studied in detail by JAGER (1971). Snails with sectioned nerves or amputated tentacles were presented with test solutions of sucrose, and their feeding behaviour was subsequently recorded. The data were used to establish the role in chemoreception of the relevant nerves and organs. Knowledge con- cerning the nervous pathways involved in chemically induced feeding behaviour is profitable for further (electrophysiological) work on the nervous control of feeding and, more particularly, its basic component, the eating movement cycle.

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