PHOTOGENIC MARINE ANIMALS. 7 



familiar examples, and it is only necessary to lift a handful of 

 such as are captured by the deep-sea liners or trawlers at night 

 to see the whole mass glittering with a hundred stars. None, 

 indeed, as the late able and conscientious observer, Mr. Hincks, 

 says, excels the common Obelia geniculata, which forms pigmy 

 forests on the broad blades of the tangles. In the fresh speci- 

 mens a touch during July causes a large number of luminous 

 points to appear, the stems most irritated exhibiting beautiful 

 flashes, which glitter like faintly dotted lines of fire, the points 

 not being boldly separated, but blending into each other ; whilst 

 the shock imparted by the instrument detaches the minute 

 Medusa-buds, which scintillate from the parent stem upwards to 

 the surface of the water. By blowing on the surface where 

 tangles abound the pelagic buds at once emit light. Moreover, 

 these minute bodies, along with various species of Ceratium, are 

 sometimes swept by gales landward, and cause luminosity in un- 

 wonted quarters. Thus the late Dr. Cowie, of Lerwick, when 

 riding at night along Deal or Dale's Voe, in Shetland, during the 

 presence of a south-westerly gale, happened to touch his beard, 

 when it and his hand gleamed with phosphorescent points, a 

 feature akin to the old experiment of Pliny, viz. rubbing Medusae 

 on a plank of wood. The gale had swept the spray and its 

 minute inhabitants on the person of the rider. In the same 

 way Vaughan Thompson found luminous patches on the masts 

 and windward yardarms on board ship, and they gradually 

 mounted upward as the gale increased. Many of the free 

 Medusa-buds are as luminous as the polyps, and the light (e. g. 

 in Thaumantias) gleams round the margin of the disc and along 

 the four radii. 



Giglioli mentions that certain oceanic forms, viz. Siphono- 

 phora, are likewise characterized by phosphorescence. Dr. 

 Bennett and the same author also found the coralligenous 

 Actinozoa and Madrepores luminous, the light in the latter 

 being greenish and lasting some minutes. The Acraspedote 

 Medusae show many luminous species (e.g. Pelagia, Rhizostoma), 

 though neither of the common forms on our coasts (Aurelia and 

 Cyanea) present this feature. In the luminous Medusae the 

 presence of certain cells containing highly refractive granules 

 akin to fatty cells has been demonstrated.* On stimulation the 



* Watase. 



