130 THE SENSES OF ANIMALS 



light of different colours, and some kinds are relatively in- 

 sensitive to light of longer wave-length at the red end of the 

 spectrum. At the aquarium in the London Zoo advantage 

 has been taken of this "blindness" to red light to trick 

 Plumose anemones into staying fully expanded all day. The 

 Plumose is a particularly beautiful anemone; it is a large 

 species, as much as six inches high, and the stalk is crowned 

 with a feathery fringe of innumerable tentacles which are 

 well likened to a head-dress of ostrich plumes. It is plentiful 

 round the British coasts, in deep water rather than the tidal 

 zone, and lives at depths where the intensity of daylight is 

 reduced by twenty fathoms or more of sea-water. Only 

 small and presumably young examples are found in the 

 region between the tides, and there they are almost always 

 confined to the gloom of a sea-cave or the water channels 

 under a huge boulder. In colour the Plumose anemone 

 ranges from olive-brown through pale orange, salmon-pink, 

 and cream, to pure white. Gosse calls it the noblest of our 

 native sea-anemones; "when we see a full grown specimen 

 of some of the more delicately coloured varieties, — the pale 

 orange, the flesh-coloured, or the clear white, — rising erect 

 from its broad base like the stem of a massive tree, crowned 

 with its expansive disc of myriad tentacles, we cannot but 

 consider it a most noble, as well as a most lovely object." 

 Gosse goes on to say that although the species is not very 

 shy of daylight, "if you would make sure of seeing it in all 

 the gorgeousness of its magnificent bloom, visit your tank 

 with a candle an hour or two after nightfall." He apparently 

 did not know that red light is as good as darkness to the 

 creature, and he would have been delighted to see the dis- 

 play that it makes in the aquarium when brightly lit with 

 many-candle-power of red light. 



The anemone responds to changes in the intensity of light 

 because when light falls on certain of the sense cells in the 

 skin it produces a chemical change in them. As a result a 

 stimulus is sent into the nerve network, which causes the 

 muscular cells to contract or relax when it reaches them. 

 The nerve network is so important in regulating the responses 

 of the animal to the stimuli reaching it from outside that we 

 must look at it more closely. The network consists of cells 



