FIXED LUMINARIES OF THE SEA. / 27 



the long axial stem is pinched, a seemingly protestings^fight 

 appears on the lowest branchlets nearest the stem, quickly ^^ 

 spreading, as if the polyps were igniting. When all those 

 on a branch have become luminous, the light begins to appear 

 on the next, and so on in succession until the whole glows 

 brilliantly. Four-fifths of a second occur between the stimu- 

 lation and the appearance of the light ; so that in a sea-pen 

 six and one-tenth inches in length, two seconds and a fifth 

 were required for its complete illumination. By pinching 

 the top or opposite end of the colony, the same phenomenon 

 resulted, but reversed. If a polyp at the end of a branchlet 

 was irritated, light immediately appeared, passed to its neigh- 

 bor, and so on ; if a branch was touched at both ends, the 

 light followed the act, and met in the centre. 



These interesting experiments, which were made by Pan- 

 ceri, can be varied in many ways by those fortunate in 

 securing a live sea-pen. 19 



The sea-pen Pavonia 20 is noted for its light-emitting prop- 

 erties ; and during the voyage of the English ship " Porcu- 

 pine " the naturalists on board had many opportunities for 

 observing its display. Sir Wyville Thompson, who was in 

 charge, says, " Coming down the sound of Skye from Loch 

 Torridon on our return, we dredged in about one hundred 

 fathoms ; and the dredge came up tangled with the long pink 

 stems of the singular sea-pen. Every one of these was em- 

 braced and strangled by the twining arms of an Asteronyx,- 

 and the round soft bodies of the star-fishes hung from them 

 like plump ripe fruit. The Pavonarice were resplendent with 

 a pale lilac phoshorescence, like the flame of Cyanogen gas ; 

 not scintillating like the green light of some sea-stars, 22 but 

 almost constant, sometimes flashing out at one point more 



