ENDOCRINOLOGY OF CRUSTACEANS 175 



ology. The reader is referred to recent reviews by Brown (1952) and by 

 Scharrer (1952). Three of the older review papers (Kleinholz, 1942; 

 Brown, 1944; Panouse, 1947) examined the problems of crustacean en- 

 docrinology. Summaries of many of the papers given at the Symposium 

 on Neurosecretion at Naples in 1953 are contained in the supplement to 

 Vol. 24 of the Puhblicazioni della Stazione Zoologica di Napoli. 



Molting Hormones 



Among crustaceans, as in arthropods generally, growth is a discon- 

 tinuous process ; the external skeleton is shed, and a new skeleton formed ; 

 increase in size is restricted to the period between the casting of the old 

 skeleton and the secretion and hardening of the new one. Between ecdyses 

 may be an interval (of varying duration in different species) of lack of 

 growth usually designated as the intermolt interval. Molting may be 

 seasonal or continuous. As might be expected, the casting of the external 

 skeleton in molting is only an outward superficial indication of a veritable 

 metabolic upheaval that occurs at this time. A subsequent paper in this 

 symposium will discuss these metabolic features in more detail. (Scheer). 



The rediscovery (Abramowitz and Abramowitz, 1938, 1940; Brown 

 and Cunningham, 1939; Smith, 1940; Kleinholz and Bourquin, 1941) of 

 observations made earlier by Zeleny ( 1905) and by INIegusar ( 1912), that 

 eyestalk removal shortened the intermolt period in crustaceans, was the 

 stimulus for the considerable number of recent studies inquiring into the 

 physiology of this process and the possibility of its control by hormones 

 originating in the eyestalk. While most of the studies cited above con- 

 cerned themselves chiefly with the effects of eyestalk removal on molting. 

 Brown and Cunningham were the first to present evidence that the accel- 

 erated molt of eyestalkless animals was due to the removal of a molt-in- 

 hibiting hormone that apparently occurred in the sinus glands ; these 

 authors found that, when the sinus gland was implanted into the body of 

 eyestalkless crayfish, the usual accelerated molt was delayed. 



Drach (1939, 1944) described a series of morphological stages that 

 occurred in the interval between two molts of crustaceans, and in his later 

 study investigated the effects on molting in Leander when the eyestalks 

 were removed during most of these stages. Drach's observations are worth 

 summarizing here because they established criteria for subsequent investi- 

 gations of this process and indicated that it was a matter of considerable 

 importance at what stage during the intermolt period eyestalk removal 

 was done. Drach found that the normal molt cycle could be divided into a 

 number of stages based on morphological characteristics, which he desig- 

 nated by the letters A, B, C, and D. In stage A the exoskeleton was very 

 soft, in stage B the branchiostegites were supple ; stage C could be divided 



