192 INVERTEBRATE PHYSIOLOGY 



the neural gland passes to the central nervous system (the neural ganglion) 

 by a nonvascular route, and that the efferent pathway of the gametokinetic 

 reflex consists of a nervous discharge along nerves to the gonads, effecting 

 release of gametes. The high concentration of the Ciona extract (1,000 

 glands) injected into 9 animals may raise some question as to whether this 

 is a true physiological hormone effect ; the nervous efferent portion of the 

 proposed gametokinetic reflex could be tested by electrical stimulation of 

 the effector nerve from the ganglion to the region of the gonad. 



Summary 



Hormonal factors have been indicated in the regulation of some physi- 

 ological processes among crustaceans : molting and associated metabolic 

 phenomena ; retinal pigment migration ; chromatophoral behavior in color 

 change ; and some aspects of reproductive physiology. The application of 

 critical standards of experimental methodology^ reveals that, despite an 

 abundant literature in the areas mentioned, conclusive proof of endocrine 

 intervention in some of these processes is lacking. 



Molting among crabs and crayfish seems to be influenced by a molt- 

 inhibiting hormone originating in the sinus gland-X-organ complex, al- 

 though some investigators, studying Mediterranean prawns, fail to reveal 

 evidence for a molt-inhibiting hormone and postulate instead a molt- 

 accelerating hormone. On the other hand, preliminary evidence for the 

 origin of a molt-accelerating hormone in a newly described structure, the 

 Y-organ, has been presented for the crab, Carcinus. It is possible that 

 these two structures may be interrelated in controlling the molt cycle of 

 crustaceans. 



Most of the studies of endocrine factors in the regulation of the retinal 

 pigments of crustaceans have been made on crayfish and prawns. For the 

 distal retinal pigment, there is direct evidence, although not unequivocal, 

 that movement of this pigment into the light-adapted position in prawns 

 is mediated by a hormone from the sinus gland ; studies of the kinetics of 

 Hglit and of dark adaptation in Palacmonetes point to the possibility of a 

 hormone that causes dark adaptation of the distal retinal pigment. Hor- 

 monal regulation of the proximal and the reflecting retinal pigments has 

 been less certainly demonstrated. 



Deficiency experiments and injection experiments point to the sinus 

 gland as the source of chromatophorotropins. The evidence for a source of 

 chromatophore-activating hormone outside the crustacean eyestalk is less 

 satisfactory, being adduced predominantly from histological studies and 

 the injection of extracts of central-nervous-system tissues; technical diffi- 

 culties make deficiency experiments less feasible than with the sharply 

 circumscribed sinus gland. 



