454 



WILLIAM G. VAN DER KLOOT 



released at the axon endings, which are collected together to form the sinus 

 gland of the eyestalk. One of the hormones released in the sinus gland is 

 molt-inhibiting. The hormone acts by inhibiting the secretion of the Y organ, 

 which is in the cephalothorax (Gabe, 1953; Echaher, 1959). The hormone 

 from the Y organ acts on the tissues to promote growth and molting. There- 

 fore, when the eyestalks are removed, the molt-inhibiting hormone is no 

 longer present, the Y organ is free to secrete, and the animal molts. It is 

 becoming clear that environmental stimuli are important in determining the 

 rate of secretion by the neurosecretory cells (Bliss, 1956). 



In the prawns the control system is somewhat more complicated. Both 

 molt-inhibiting and molt-accelerating hormones are produced by neuro- 

 secretory cells and released in the eyestalk. The molt-accelerating hormone 

 also acts by stimulating the Y organ (Fig. 6). In these animals then, the removal 



NEUROSECRETORY CELLS 



in ganglionic X- organ and CNS 



molt-inhibiting 

 hormone 



molt-accelerating 

 hormone 



^^^ 



Y ORGAN 



molting hormone 



BODY TISSUES 



(promotes growth, differentiation, and molting) 



Fig. 6. A diagrammatic summary of the control of molting in the prawn, 

 Palaemon (Carlisle, 1959). 



^> excitatory hormone; ---^ inhibitory hormone. 



of the eyestalks gives a measure of the relative dominance of the two hor- 

 mones. In Palaemon (=Leander) sirratus collected in Roscoff, removing the 

 eyestalks accelerates molting (Drach, 1944; Carlisle, 1959). The same opera- 

 tion on the same species collected at Plymouth slows molting. The dominant 

 hormone at Roscoflf is inhibitory, at Plymouth excitatory (Carhsle, 1959). 

 If there are any differences between Roscoff and Plymouth leading to the 

 selection between acceleration and delay, they are unknown. 



