214 INVERTEBRATE PHYSIOLOGY 



division of the cycle into four major phases : A, the period of absorption of 

 water and increase in size ; B, the period of hardening of the integument ; 

 C, the period of completion of the integument, tissue formation, and storage 

 of reserves ; D, the period of preparation for the molt. 



Scudamore (1947) was first to observe that oxygen consumption in- 

 creases prior to a molt in the crayfish Camharus propinquus. Edwards 

 (1950) also found, in Uca pugilator and U. pugnax, a diurnal cycle of 

 oxygen consumption, with a maximum at night ; the latter cycle corre- 

 sponds with the cycle of motor activity. Brown, Bennett, and Webb ( 1954) 

 cibserved this diurnal rhythm, and in addition tidal, semilunar, and lunar 

 rhythms. Scheer and Scheer (1954b) have recently examined the premolt 

 increase in oxygen consumption in Leandcr scrratus, and have found that 

 it is not simple. For animals in the Ci to Co stages of Drach (1944), we 

 find an oxygen consumption of 14.47 /xl per animal per hour after correction 

 to mean body weight. For an animal of the same size in stage D,, in which 

 the resorption of the inner layers of the old integument is beginning, the 

 oxygen consumption rises sharply to 18.52 ;ul/hr. The rise is transient, 

 however, and in stage Do, marked by formation of the principal layer of 

 the new integument, the value falls again to 13.29 />il/hr. Finally, in stage 

 D3, immediately preceding the molt, when the new integument is fully 

 formed and absorption of the inner layers of the old integument is com- 

 pleted, there is a second rise to 17.64 /xl/hr. Whether this complexity is 

 typical of other decapods is uncertain ; it is clear that the hormonal factors 

 operative in the Neapolitan race of Leandcr scrratus are qualitatively 

 different from those observed in many other decapods, even in other races 

 of the same species. 



Evidence for the hormonal control of molting was obtained by Megusar 

 (1912), but was not interpreted as such. Brown and Cunningham (1939) 

 showed that removal of the eyestalks from crayfish {Camharus immunis) 

 is followed by molting at an earlier date than in normal controls, and that 

 implantation of sinus glands delays molting in eyestalkless animals. At 

 that time, there was evidence that the sinus glands in the eyestalks are 

 endocrine in function, and a molt-inhibiting hormone, formed in the sinus 

 glands, was postulated to explain the observations of Brown and Cunning- 

 ham (1939). The accelerating effect of eyestalk removal on molting has 

 been reviewed by Passano (1953), who has also provided evidence that 

 the molt-inhibiting factor is formed by neurosecretory cells in the X-organ 

 of the eyestalk, and liberated from the sinus glands. The same conclusion 

 was reached independently by others, and their results are reviewed by 

 Passano (1953). Drach (1944) has established for the Roscofif race of 

 Leander scrratus that eyestalk removal is only effective in shortening the 

 intermolt cycle when the operation is performed before stage Di ; this 



