IN FEATHERS AND FUR. 317 
the water, fishes at the depth of eighteen feet could be readily seen 
by it, and half a dozen of the individuals which make up the float- 
ing colony, will light up a ship's cabin enough to enable one to 
read. The light is of a greenish hue. The Pyroseua is shaped 
like a long cylinder, and it moves through the water by the force of 
the water thrown out all the time, for though they are floating 
about, they eat all the time like the rest of the family. 
Another of the Tunicates is the Salpa. In this, the individuals 
are united in long chains, which glide through the water with a 
peculiar motion like a serpent. Sailors often call them sea snakes. 
They move by the same means as the Pyrosena, the current of 
water which each one of the chain throws out. They work to- 
gether like a machine, each drawing in and throwing out at the 
same moment with all the rest. 
When a chain of Salpas is broken, each one can live by itself, 
and any attempt to get them out of the water separates them at 
once. 
There's another curious thing about this family. The young 
of these chain Salfas are always solitary, and their young are the 
chained family again. 
Salfas are found in the Mediterranean sea, and in the Equa- 
torial seas. They live some ways below the surface usually, but 
on calm nights they come to the surface. 
