418 SUPPLEMENT ON ACEPHALA. 
to the division of Zoophytes. They are most generally 
grouped, either in a circle or ellipsis, sometimes pretty regu- 
larly; but some are also found which may be said to be 
scattered, two or three only being together. They have much 
of the exterior of radiated animals. 
In the curious compound genus called Pyrosoma, the 
organization of each little animal composing the whole, has a 
very great analogy with that of the salpz. In fact, we can 
scarcely be assured even yet, that the pyrosomata may not be 
young salpz, not yet adult, and which disunite themselves 
later. According to the actual state of our information, the 
pyrosomata form cylindrical masses, more or less elongated, 
soft, gelatinous and bristling at their surface, with a great — 
number of sorts of spines, or pointed tubercles, a little more 
hard, or more cartilaginous than the rest. ‘These masses, 
which float horizontally in the interior of the sea, are, doubt- 
less, abandoned to its movements, and cannot resist them, nor 
direct themselves. Accordingly, they are never to be met 
with but in the open sea, and often in troops, composed of a 
great number of these masses. Nothing can be more brilliant, 
sparkling, and lively, than the phosphoric light which these 
animals emit. They often form long trains of fire, from the 
manner in which the masses are disposed in cordons. But a 
more singular phenomenon attached to this phosphorescence, 
is, that the colours vary instantaneously, passing rapidly from 
the most lively red to the principal tints of the solar spectrum, 
to the crimson of the morning, to orange, to greenish, to 
azure-blue, and finally to an opaline yellow, when the mass 
is, to all appearance, in a state of absolute repose. 
