544 



THE WONDER OF LIFE 



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



.a 





Fig. 87. — ^Muoh branched chromatophore of a prawn, Praunus flexuoxua, 

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

 or contracts centripetally. The chromatophore 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, PalcBmon treillianus 

 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. 

 "When ov,e is put into a white porcelain vessel it beconiQSi 



