4 W. C. M'Intosh on the Abyssal Theory of Light. 



in July off many of our shores where Laminarias abound, 

 produces phosphorescence from a vast number of minute 

 medusa-buds. The same takes place most strikingly in ves- 

 sels in which specimens of Ohelia geniculata attached to 

 tangle-blades are immersed. On touching the seaweed, a large 

 number of such luminous points appear on the zoophytes, the 

 stems most irritated sending off beautiful flashes, which glitter 

 like a faintly dotted line of fire, the points not being harshly 

 separated, but blending into each other ; while the shock im- 

 parted by the instrument detaches the minute medusa-buds, 

 which scintillate from the parent stem upwards to the surface 

 of the water. Dr. Allman would therefore have found this a 

 much more interesting species for his observations than 0. 

 dichotoma *. The immense abundance of these minute phos- 

 phorescent organisms (medusa-buds) in some parts of the 

 Zetlandic seas may explain the following fact, reported to me 

 by Mr. Gatherer, the intelligent naturalist of Fort Charlotte, 

 Lerwick. Dm'ing the prevalence of a south-easterly gale, the 

 late Dr. Cowie, of Lerwick, was riding at night along Deal's 

 (or Dale's) Voe, when, happening to touch his beard, he found 

 both it and his fingers gleam with phosphorescent points ; and 

 the same ensued on rubbing his sleeve. The gale had proba- 

 bly swept the spray and thousands of its minute inhabitants 

 landwards, and showered them on the person of the rider. 



If Thaumantias^ or any other phosphorescent Medusa, which, 

 when swimming freely, has its disk-margin shining like a 

 dotted fiery ring of great beauty, be taken from the water and 

 rubbed on a woollen surface, such as a carpet, a considerable 

 luminous area is produced, showing that the entire mass of 

 the animal has this property when thus violently irritated ; 

 moreover the surface just mentioned, as well as the fingers, 

 remain in a gleaming condition for some time. I am aware that 

 this view slightly differs from that of so distinguished and so 

 cautious an observer as my friend Mr. Busk, who, along with 

 Dr. Allman and probably Panceri, confines the seat of light to 

 the marginal tentacular bulbs ; but I cannot conscientiously say 

 otherwisef. If Be^-oe be treated in the same rough manner, 

 it is found to be less phosphorescent, and the luminosity of 

 the area disappears sooner. It did not signify, in any case 

 observed by me {Beroe excepted, as I did not examine it es- 

 pecially on this point), whether the examination were made at 



* This author (Proc. Roy. Soc. Edinb. vol. iv. p. 519) is of opinion that 

 Beroe and other Ctenophora are among- the chief sources of the phos- 

 phorescence of the sea in our latitudes. 



t The state of matters in Aphlebina, where the light gleams along the 

 simple tentacular processes, supports this view. 



