92 



KINETIC HORMONES — I 



level to some lower maintenance one". Conversely, a white-to- 

 black change would result in an abrupt discharge of PDH, which 

 would become similarly reduced to some lower level as adaptation 

 became complete. "The introduction of large amounts of either 

 factor, in the presence of a somewhat lower titre of the second, 



12 3 



Time, hr 

 Fig. 3-17. Effects of extracts containing Palaemonetes-iAGYiT^i^Y^G 

 and -DARKENING HORMONES, PLH and PDH, on the red chromato- 

 phores of the prawn, Palaemonetes. Pigment dispersion is shown 

 with time in hours, on a much less extended scale than Fig. 3-16; 

 the extracts are less concentrated and act more slowly. Curves i, 

 ii and iii show effects in eyestalkless specimens with initially dis- 

 persed pigment: curve i: the effect of PLH injected at time wears 

 off and is unaltered by subsequent injection of seawater at the time 

 marked by the arrow; curve ii: PLH injected at time followed 

 by PDH, instead of sea water, injected at the arrow, shows the rapid 

 dispersing effect of PDH; curve iii: PDH injected at time pro- 

 duces a slight concentration due to shock and a rapid return to 

 full dispersion. This last is compatible with a dispersing effect 

 of PDH, but does not prove it alone. Curve iv shows that injection 

 of PDH only partly overcomes the natural supply of PLH in a 

 normal specimen exposed to light on a white background. PLH 

 was obtained from sinus glands and tritocerebral commissures. 

 PDH was obtained in least contaminated form from the abdominal 

 ganglia (from Brown, Webb and Sandeen, 1952). 



