ROMANCE OF DEPTHS OF THE SEA 123 



these surface organisms capable of producing 

 phosphorescence be kept in an aquarium in a 

 dark room the same remains true. Although 

 they are exposed to no secular change of light 

 and darkness, they only show their lights at a 

 time when the outside world is dark. The same 

 is true, as Gamble and Keble have shown, with 

 the chamaeleon-shrimp, which in the sea shows 

 a variety of protective colouring during the 

 daytime but at night becomes a transparent blue. 

 Hence it is obvious that the tide has produced -an 

 effect which is lasting on certain organisms even 

 when they have been removed from their natural 

 surroundings and from the tidal influence for 

 considerable periods. 



Then again we have a rhythmical change of 

 temperature, which is fairly constant for given 

 places in the sea. About February and March 

 the sea is at its coldest, but it gradually warms 

 up until in August it attains its highest normal 

 temperature. Of course in all these rhythms 

 there are many disturbing features, such as the 

 weather. But these can fairly easily be dis- 

 counted. Just as we have an annual rise and 

 fall of temperature, so do we have a daily one, 

 the temperature being at its lowest about sun- 



