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The role of the posterior tentacles of the giant African land snail, Achatina fulica Bowdich (Gastropoda: Pulmonata), in olfaction and orientation
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|Title:||The role of the posterior tentacles of the giant African land snail, Achatina fulica Bowdich (Gastropoda: Pulmonata), in olfaction and orientation|
Tentacles of the giant African land snail, Achatina fulica
|Authors:||Ichinose, Lester Yoshio|
|Keywords:||Giant African snail|
|Abstract:||The role of the posterior tentacles of the giant African land snail, Achatina fulica Bowdich, in olfaction and orientation was studied in a three-part investigation; anatomy, behavior and exectrophysiology. Anatomical studies revealed a close homology with other stylommatophore pulmonates. A freely moving tubular retractor muscle attached distally inside the tentacle tip contains the tentacular artery, and the optic and tentacular nerves. The latter nerve connects with the procerebrum proximally and with a ganglion distally. The ganglion sends digitiform branching projections throughout the tip epithelium, where they receive afferent fibers from bipolar cell aggregates in the sub-epithelial region. A second set of 4-6 afferent nerves serving the ventro-lateral epithelium of the tentacle tip was found to insert between the ventral digitiform projections, and extend to bipolar cell body aggregates in the subepithelial region. These "chemotactile" nerves extend centrally along the ventro-lateral wall and undergo several bifurcations at the base of the tentacle, forming a complex nerve net as a result. The left and right peritentacular nerves, which terminate proximally in the posterior procerebrum, receive the bifurcations from chemotactile nerves serving the left and right ventrolateral epithelium of the tip, respectively. They also receive bifurcations from the same ventral (middle) chemotactile nerve. The bipolar cell aggregates mentioned above send distal fibers to the tentacle tip epithelium. They extend between the columnar epithelial cells and terminate at the cuticle in these types of nerve endings: 1) Blunt, expanded endings terminating at the cuticle base; 2) bifurcating nerve endings within the cuticle; 3) 5-7 filamentous unbranched endings in the cuticle, apparently emanating from a sub-cuticular conical sheath. The olfactory ability of eight l½ year old laboratory raised snails was investigated by noting their behavior in a four-choice biradially symmetrical maze. A vial containing vegetable juice serving as the stimulus was randomly placed in front, rear, left, and right of the snail in known ratios. The remaining vials contained distilled water, and the maze was entirely darkened during a trial. 68% of the total trials demonstrated positive chemotaxis for this group. For the experimental group, the epithelium of the posterior tentacles was removed in 7 members of the normal control group. Positive chemotaxis for the experimental snails occurred in 25% of the total trials. Two cerebropetal channels serving olfaction were demonstrated in electrophysiological experiments on isolated posterior tentacles. Tentacular nerve activity increased with odor stimulation, but no adaptation was evident up to the time the experiment was terminated 5.5 minutes later. No activity was noted in response to tactile stimuli. The activity of the chemotactile nerves increased when olfactory and tactile stimuli impinged on the tentacle tip; the activity in response to the olfactory stimulus diminished 80-120 seconds after the introduction of the odor. The ability of a single posterior tentacle to provide directional information in response to olfactory and tactile stimuli was demonstrated electropbysiologically on the chemotactile nerves.|
Thesis (Ph. D.)--University of Hawaii, 1968.
Bibliography: Leaves 82-86.
ix, 86 leaves illus., tables
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|Appears in Collections:||Ph.D. - Zoology|
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