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- 







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 gland have no such action. When sinus gland 

 implantations are discontinued, gastroliths begin to form about a week after 

 the last implant, indicating that the implanted glands are no longer effective. 



Histological changes in the sinus glands of crustaceans have been shown 

 to be correlated with the molt cycle. ^-^ Just prior to molt, acidophilic secre- 

 tory granules appear to be the predominant ones; after molt completion, 

 basophilic ones are more prevalent. 



The molting process which is set into operation by eyestalk removal re- 

 sembles still further the changes observed in normal premolt animals. ^"^^ 



