700 Comparative Animal Physiology 



The sources of the chromatophorotropins involved in these reactions of 

 animals lacking the sinus glands are within more or less restricted regions 

 of the central nervous system and its sheaths (Fig. 265). Extracts of central 

 nervous systems of certain species of Group I, on injection, lighten eyestalk- 

 less specimens and concentrate white pigment.-^' ^° Similarly extracts of the 

 central nervous system of Uca, of Group III, darken eyestalkless specimens of 

 IJca and simultaneously concentrate white pigment. Extracts of the ner- 

 vous svstem of Crago, of Group II, lighten the body and darken the telson 

 and uropods while concentrating white pigment. Therefore, in all three 

 groups, injection of extracts of central nervous system organs produces the 

 same major results as strong stimulation of the eyestalks. No source of 

 chromatophorotropins needs to be sought outside of the central nervous 

 system. 



A careful survey of the central nervous system of Crago shows by far the 

 major portion of the telson-darkening and uropod-darkening action, as well 

 as body lightening, resides in the minute tritocerebral commissure of the 

 head region (Fig. 266). The remainder of the central nervous system, how- 



- TMOflACIC coto 



Fig. 266. Diagram of the anterior region of the crustacean central nervous system showing 

 the position of the tritocerebral commissure. From Brown, 1948. 



ever, possesses significant body-lightening activity.-'* This latter fact, together 

 with the discovery that an alcohol-soluble fraction of the tritocerebral com- 

 missures possesses very strong body-lightenmg and no "tail"-darkening activ- 

 ity, while the alcohol-insoluble fraction causes strong "tail"-darkening and 

 simultaneously strong body-darkening,-'^^ establishes the presence of two 

 chromatophorotropins in Crago nervous systems (Fig. 267). One lightens 

 the body but not the "tail" of Crago, and hence has been called Crngo-body- 

 lightening hormone (CBLH); the other, in the presence of CBLH, darkens 

 only the "tail," but in the absence of CBLH darkens the whole body and 

 is hence called Crago-darkening hormone (CDH). We can now see the 

 probable cause of the striking difference between strong and weak stimula- 

 tion of the eyestubs in this species. Strong stimulation appears to induce the 

 liberation of both principles, whereas weak stimulation liberates almost ex- 

 clusively CDH. 



