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 also 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. Supraoesophageal and suboesophageal brain fractions both have a greater effect than whole brain; both fractions may contain factors affecting shell growth. Suboesophageal fractions from shell-repairing donors show a reduced effect. A supraoesophageal factor may be involved in normal shell growth and a suboesophageal factor in shell repair.
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