The sinus glands of the Brachyura are composed of swollen nerve fiber endings, which store and release secretory material synthesized within cells of the eyestalks, the brain and probably the thoracic ganglionic mass. Removal of the sinus glands from the land crab, Gecarcinus lateralis, does not induce molt, because sinus glands are reservoirs, not sources, of molt-inhibiting hormone. Increase in respiratory rate and fall in respiratory quotient, which follow eyestalk removal and signify the approach of molt, do not occur after sinus gland removal.