FACTS AND THOUGHTS ABOUT LIGHT-EMITTING ANIMALS. 233 
sea polype” (JJmbellularia groenlandica ), consisting of “twelve 
gigantic Alcyonarian polypes, each with eight fringed arms, termi- 
nating in a close cluster on a calcareous stem ninety centimetres 
high.” He states that when this splendid Pennatulid was taken 
from the trawl, the polypes and the membrane covering the hard 
axis of the stem were so brightly phosphorescent that Captain 
Maclear found it easy to determine the character of the light 
by the spectroscope. It gave a very restrictedly -continuous 
spectrum, sharply included between the lines b and d.* The same 
naturalist writes, after dredging in 828 fathoms off St. Vincent, 
that the trawl “ seemed to have gone over a regular field of a 
delicate simple Grorgonoid, with a thin wire-like axis slightly 
twisted spirally, a small tuft of irregular rootlets at the base, 
and long exsert polypes. The stems, which were from 18 
inches to 2 feet in length, were coiled in great hanks round the 
trawl beam and entangled in masses in the net, and as they 
showed a most vivid phosphorescence of a pale lilac colour, their 
immense numbers suggested a wonderful state of things beneath 
— animated corn-fields waving gently in the slow tidal current, 
and glowing with soft diffused light, scintillating and spark- 
ling on the slightest touch, and now and again breaking into 
long avenues of vivid light indicating the paths of fishes or 
other wandering denizens of their enchanted region.” f 
Again, in the “ Voyage of the Porcupine” J the same fortunate 
naturalist noticed the Sea-pen, Pavonia quadrangularis , 
which entangled the dredge with its pink stems a metre long, 
fringed with hundreds of polypes, to be “resplendent with a pale 
lilac phosphorescence like the flame of cyanogen gas, almost 
constant, sometimes flashing out at one point more brightly, 
and then dying gradually into comparative dimness, but always 
sufficiently bright to make every portion of a stem caught in 
the tangles or sticking to the ropes distinctly visible.” 
Probably the grandest display of light-emitting is by the 
great cylindrical-looking Pyrosoma , one of the Tunicata (PI. VI. 
fig. 5). This animal is really a compound one, and the common 
uniting tissue has the shape of a hollow cylinder rounded and 
closed at one end and cut short and open at the other. This is firm 
and transparent, like so much cartilage, and on its outside are 
arranged numerous whorls of separate zooids. Each zooid project- 
ing is large near the supporting cylinder and smaller where free, 
and this end has the mouth opening, whilst the base is perforated 
by holes, which are continued through the cylinder. The water 
system thus opens into the hollow cylinder, and the water issuing 
* “ The Atlantic,” vol. i. “ The Voyage of the Challenger,” p. 151. That 
is, in the green, near the less refrangible part, 
t Thomson, Op. cit. p. 119. 
f Thomson , 11 Cruise of the Porcupine,” p. 149. 
