Regulation of shell growth in the pulmonate gastropod Helisoma duryi

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Abstract
Photoperiod has a significant effect on linear shell deposition rates; animals maintained in continuous darkness (DD) deposit shell more rapidly than those held in continuous light (LL) or 12L:12D. Shell deposition is endogenously governed and might be synchronized by photoperiod. Photoperiod affects the relative proportion of shell occupied by different crystal layers. Injections of brain homogenates from fast-growing animals stimulate shell deposition in slow-growing animals. Supraesophageal and subesophageal brain fractions have a greater effect than whole brain; both fractions may contain factors affecting shell growth. Subesophageal fractions from shell-repairing donors show a reduced effect. A supraesophageal factor may be involved in normal shell growth and a subesophageal factor in shell repair.

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