MOLLUSCOlDA. 
315 
The third species, P. atlantims, was discovered by Peron and 
Tesnour in the Equatorial seas. 
These curious Ascidians are so created in rings as to constitute a 
Wig fine cylindrical tube, closed at one end and open at the other, 
hy the contraction and dilation of the mass of beings, this great 
c yhnder swims slowly through the open sea, lighting up the ocean 
with its phosphorescent light, shining through the water like a glowing 
Mr. Bennett thus describes one of these pelagic appearances : 
1 On the 8th of June, being then in lat. 3(P S. and 27 5 W. long., 
Wing fine weather and a fresh south-easterly trade-wind, and the 
thermometer ranging from 78° to 84°, late at night the mate of the 
Watch called me to witness a very unusual appearance in the water. 
This was a broad and extensive sheet of phosphorescence extending 
from east to west as far as the eye could reach. I immediately cast 
the towing-net over the stem of the ship, which soon cleaved through 
the brilliant mass, the disturbance causing strong flashes of light to 
he emitted, and the shoal, judging from the time the vessel took m 
Passing through the mass, may have been a mile in breadth. On 
taking in the towing-net, it was found half filled with Pyrosoma 
a tta ntious, which shone with a beautiful pale greenish light. After 
the mass had been passed through by the ship, the light was still seen 
a ^ern, until it became invisible in the distance, and the ocean became 
hidden in the darkness as before this took place. 
“ The second occasion of my meeting these creatures was in a high 
latitude, and during the winter season. It was on the 19 th of August, 
the weather dark and gloomy, with light breezes from north-north- 
eas t, in lat. 40° 30' &, and 138° 3' E. long., at the western entrance 
to Bass’s Straits, and about 8 o’clock p.m., when the ship’s wake was 
Perceived to be luminous, while scintillations of the same light were 
Wndant all round. To ascertain the cause, I threw the towing-net 
° v erboard, and in twenty minutes succeeded in capturing several 
■pyrosoma, which gave out their usual pale green light ; and it was, 
110 doubt detached groups of these animals which were the occasion 
of the light in question. The beautiful light given out by these 
^olluscans soon ceased to be seen; but by moving them about it 
to uld be reproduced for some length of time after. The luminosity of 
tll<! water gradually decreased during the night, and toward morning 
^ as no longer seen.” 
