544 



THE WONDER OF LIFE 



of a shore- crab is directly influenced, while the sheU is 

 being formed after a moult, by the dominant colour of the 

 immediate environment. 



There can be no doubt that certain colour-reactions 

 which follow reflexly and necessarily often look as if they 



^,- 



FlG. 87. — Much branched ohromatophore of a prawn, Praunus flexuoxus. 

 {After Degner.) The pigment flows out along the root-like branches 

 or contracts centripetaUy. The ohromatophore seems to arise 

 from a combination of cells — a syncytium. 



should be advantageous, but it is difficult to give direct 

 proof of this. One of the prawns, Palcemon treilliamos 

 studied byFrohlich (1910) is blue^or green by day,!^when 

 its red chromatophores are strongly contracted, and reddish- 

 brown by night, when the red chromatophores expand, 

 ^heft one is put into a vhite porcelain yessel il^ becojjaes. 



