90 



KINETIC HORMONES — I 



from different spots appearing on the paper have only been tested 

 upon eyestalkless prawns kept on a white background ; in these the 

 red chromatophores are fully dispersed owing to the lack of PLH, 

 reinforced by the dispersing effect of direct light. It follows that 

 only light-adapting substances causing concentration of red pig- 

 ment can be satisfactorily identified, though by using sufficiently 

 concentrated extracts relatively rapid reactions can be obtained 

 (Fig. 3-16). Other parts of the nervous system yield extracts with 

 an action similar to that of PLH, but it is more than likely that 



time (min.) 



Fig. 3-16. Effect of extracts of the tritocerebral commissures on 

 the dispersed red pigment in the chromatophores of eyestalkless 

 prawns, Penaeus hraziliensis . The effect of sinus gland extracts 

 would be similar. The abscissae represent time in minutes after the 

 injections; the ordinates, the state of dispersion of the pigment on 

 the same scale as the melanophore index. The dotted lines show 

 that readings taken at night are closely similar to those by day, 

 shown in full lines. The extracts from the post-commissure region 

 ip.c.) are rather more active than those from the main commissure 

 (c.) in yielding a pigment-concentrating hormone, the effect of 

 which is to cause rapid pigment concentration. This wears off as 

 the hormone is destroyed in the tissues and the pigment returns 

 to its original state of dispersion (from Knowles, 1953). 



