552 F. W. (ixVMBLK. 



II. The CoLOUit-PHYSioLOGY OF Hri'POLYTE Varians. 



Previous aiialj'sis (1904) of the factors that determine the 

 wide range of sympathetic coloration in Hippolyte varians 

 has revealed : 



(1) Tliat at the time of birth the cbromatophore system is 

 constant in organisation, and offers such slight variations in 

 the amount of the only true pigment (red) as to suggest that 

 the colour of the parent does not influence that of the 

 offspring. 



(2) That the next known (adolescent) stage (4"5 mm. long) 

 presents three colour patterns : Red-lined pattern (by far 

 the most common), barred pattern (rare), Jind monochrome 

 pattern. 



(o) Tliat these young, transparent, adolescent animals 

 become green on green weed, or red on red weed within 

 forty-eight hours .if placed amongst a mass of weed sti-ongly 

 illuminated bv direct sunliy:ht. 



(4) That having assumed the tint of their surroundings 

 the young animals can be persuaded to change it witliout 

 difficidty, but tljat in latei- stages this elasticity is lost and 

 colour-change is only effected slowly or not at all. 



(5) That the adolescent colour-pattern may become the 

 adult one if the environment is kept constant, but thiit lined 

 and barred patterns are in aU probability transformed into a 

 monochrome by the filling up of the interstices upon exposure 

 to a more uniformly coloured background. These results 

 place the chief efficac}' of colour-development in Hippolyte 

 upon external factors. The eye and nervous system control 

 the response to background, but do not determine it. 

 Inheritance provides paths along which pigment develops, 

 but does not settle the colour or pattern. The young animal 

 appears plastic, but the old one is a creature of habit. 



The need for. a more careful analysis of these responsible 

 external factors and of their continued workinof has led to the 

 following results. The variability of broods born of similarly 

 and of diversely coloured parents and the prolonged action of 



