234 
POrULAH SCIENCE REVIEW. 
from it propels the whole in the opposite direction, at the same 
time that it revolves on its long axis. In the Mediterranean 
the Pyrosomes are from two to fourteen inches in length, and 
they may he three inches in diameter ; they are seen in great 
companies, and when floating and revolving just below the sur- 
face, look like incandescent rods of iron. The light is said to 
be polychroic in the Pyrosome of the Atlantic, or of a vivid 
green ; and it is azure in a gigantic species. It does not come, 
according to Panceri, from every spot on the body, but from two 
round spots, one on either side of each of the zooids, situated 
over the position of the ganglia of the nervous system, and there 
are loops like cords passing over the narrow end connecting 
them (figs. 1 and 2). They 
are placed between the two 
tunics of the integument, and 
are attached to the outer 
one. After a while the light 
becomes diffused over the 
whole surface. Panceri states 
that when the animal is not 
over-stimulated, the light is 
intermittent, and that it con- 
sists of sparks from the spe^» 
cial cells in each zooid. The 
luminous bodies are photo- 
genic structures, and produce 
an albuminoid substance, and 
also much that is soluble in 
ether. This matter may be- 
come diffused by handling, 
and retains its luminosity for 
some time. Panceri states 
that the light is increased 
by, and lasts long in fresh 
water. The largest kind of 
this wonderful light-emitting 
compound Tunicate is a 
grand sight in the night, as 
it gives out suddenly a vivid 
greenish light, large in its 
dimensions, and then it sinks 
to the depths. Moseley writes : 66 A giant Pyrosoma was caught 
by me in the deep-sea trawl. It was like a great sac, with its 
walls of jelly about an inch in thickness. It was four feet in 
length and ten inches in diameter. When a Pyrosoma is stimu- 
lated by having its surface touched, the phosphorescent light 
breaks out at first at the spot stimulated, and then spreads 
Fig. 1 . The open end of Pyrosoma yigan- 
teum , showing the zooids with 
their luminous spots. 
Fig. 2. The outer end of a single zooid, 
with luminous spots, enlarged.] 
