176 INVERTEBRATE PHYSIOLOGY 



into two substages characterized by increased rigidity of the branchio- 

 stegites and the condition of the sensory hairs along the margins of the 

 body; stage D was divided into 4 subdivisions, Di (divided into three 

 subgroups), Da, Dg, and D4, culminating in ecdysis. In a group of 340 

 Leander measuring 25-50 mm., sampled in October, the percentage dis- 

 tribution of the various stages was : A and B, 2.6^0 ; Ca, 16.7% ; Cb, 

 21.1% ; D/, 21.7% ; W, 14.1% ; D/", 6.4% ; D. and D3, 17.0%. Drach 

 found that, if the eyestalks were removed in either of the C stages or in 

 stage Di', a significant shortening of the interval between the operation 

 and the ensuing molt of these animals occurred as compared with unop- 

 erated control animals in comparable stages. After removal of the eye- 

 stalks in the subsequent Di stages or in D, or D3, molting in the operated 

 animals was not significantly accelerated over that in the unoperated 

 controls. 



The regulation of the molt cycle described above could not be clearly 

 attributed to the sinus gland if judged by the criteria used in endocrino- 

 logical analyses ; it was generally agreed that eyestalk removal accelerated 

 molting, and that implantation of sinus glands into eyestalkless animals 

 delayed or prevented this accelerated molt, but the additional demonstra- 

 tion was lacking that removal of the sinus glands alone would efifect the 

 same acceleration of molting as was accomplished by removal of the eye- 

 stalks. A series of three independent studies published simultaneously 

 (BHss, 1951; Havel and Kleinholz, 1951; Passano, 1951b) showed that 

 careful surgical removal of the sinus glands, leaving the rest of the eye- 

 stalk undamaged, had no accelerating efifect on molting or on some of the 

 metabolic processes associated with molting. These results were in striking 

 contrast to the accelerated molt obtained with removal of the entire eye- 

 stalk. An explanation of these differences was offered by the studies of 

 Passano (1953), who questioned the acceptance of the specific endocrine 

 function of the sinus gland in accelerating molting; he postulated that, 

 since removal of the sinus gland itself had no effect on inducing precocious 

 molting, the delay in precocious molting seen after sinus-gland implanta- 

 tion might have been due to a nonspecific chemical effect rather than to 

 hormonal action. By a series of localization experiments Passano demon- 

 strated that removal of the X-organ induced accelerated molting in the 

 crabs Uca, Callinectes, and Sesarma, and that implantation of the medulla 

 terminalis, which includes the X-organ, prevented or delayed induced 

 molting. 



The role of the X-organ in crustacean endocrinology had been obscure 

 for the twenty years following its discovery by Hanstrom. The investiga- 

 tions described above not only revealed the physiological activity of this 

 organ in the molting process, but Bliss and Passano proposed that the 



