238 THE WONDER OF LIFE 



The brain is not required at all, which corroborates the 

 observation of Bethe, that a crab in which the connexion 

 between the brain and the ventral nerve cord has been cut, 

 can walk and select its food and take its meals, and defend 

 itself very much as usual. So, after the complete severance 

 of the brain, one of Minkiewiez's spider-crabs was often 

 seen to disguise itself, executing the whole series of move- 

 ments in the proper order. 



The power of discriminating between different rays of 

 light is well seen in many animals. Minkiewiez has shown 

 that the newly-hatched larvae (Zosese) of the spider-crab 

 (Maja squinado) are strongly attracted to the light, and 

 under a spectrum make for the rays of the shortest wave- 

 length the violet and blue. The red Nemertean worm, 

 Linens ruber, is negative with respect to diffused light, 

 but when it is illumined by coloured light it makes for 

 red and yellow rays and is repelled by the blue and green. 

 In diffused light in an aquarium with a floor of two colours 

 (say red and violet), it comes to rest on the red and avoids 

 the violet. If the colour be other than red and violet, it 

 always seeks out the background nearest red. 



Hermit-crabs seem to be very suitable animals for experi- 

 mentation, as they do not get excited and can be shifted 

 about and placed here and there in an aquarium while 

 within the shelter of their shell. They show a strong- 

 preference for a white background, and next to that for 

 a green one. Apart from green, the attractive value of a 

 colour corresponds to its position in the solar spectrum. 

 In an aquarium with a floor half green, and half any other 

 colour but white, the hermit crabs make for the green 

 side whenever they get their eyes out of their sheltering 

 shell, and Minkiewiez found that during the day they never 



