. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Endocrine Mechanisms 739 glands from other crayfishes are implanted into the abdomen of such eye- stalkless specimens, molting will be delayed beyond the time of that of the controls.^^' ^'^ Similar implantations of eyestalk tissue from which the sinus gland has been removed are without appreciable molt-retarding influence. Removal of only one eyestalk results in a slightly accelerated molt, suggest- ing the eff^ect to be quantitative in character. A molt-inhibiting role of the crustacean sinus gland has receive
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Endocrine Mechanisms 739 glands from other crayfishes are implanted into the abdomen of such eye- stalkless specimens, molting will be delayed beyond the time of that of the controls.^^' ^'^ Similar implantations of eyestalk tissue from which the sinus gland has been removed are without appreciable molt-retarding influence. Removal of only one eyestalk results in a slightly accelerated molt, suggest- ing the eff^ect to be quantitative in character. A molt-inhibiting role of the crustacean sinus gland has received confir- mation in studies of the control of gastrolith formation in crayfishes (Fig. 282). These concretions, normally produced only during the premolt per riods, may be caused to form at any other period of the year by excision of both eyestalks or by surgical extirpation of the sinus glands by themselves.^^^- ^'^ After eyestalk removal during a non-molting period, such as between Sep- tember and March, the gastroliths commence to form in less than 24 hours at about 20° C. and then increase in size slowly during eight to ten days, 20- .20 O 10 2 0- MOLT I -60 UJ r MOLT II 5 0- o-^^-Q- 0. 15 20 25 TIME IN DAYS Fig. 282. A, Increase in gastrolith size and molting in crayfishes after removal of the eyestalks with their included sinus glands. Note that an animal once molted proceeds almost immediately to prepare for another molt. B, Eyestalkless crayfishes into which sinus glands are implanted at three or four-day intervals show no gastrolith production. From Scudamore.^*^ thereafter accelerating rapidly up to the time of molt, which usually occurs between the fifteenth and twentieth days. Those individuals which survive the molt immediately proceed to form a new set of gastroliths. If, however, one implants a sinus gland into the abdominal region of eyestalkless animals at three- or four-day intervals gastrolith formation is suppressed. Eyestalk tissues other than the sinus gl
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