SEA-SQUIRTS. 147 
Nervous System.—In the simplest forms, the nervous 
system consists of a simple cord ganglion, between the two 
body-openings. 
Development.—They multiply by eggs and by budding; 
the young in some cases assuming at first a free-swimming 
tadpole form (Fig. 185, a), finally becoming attached, a’, 
the tail ¢ absorbing, and the animal assuming the adult 
form B. 
Pyrosoma.—The pyrosoma (Fig. 186), or fire-body, is 
a gigantic compound ascidian, sometimes five feet long, 
twelve inches across, with walls three inches thick. It is 
a colony of ascidians forming a cylindrical, barrel-shaped 
Fic. 186.—Pyrosoma gigas, a luminous compound ascidian, 
object open at one end. Here the circulation of water 
aids in locomotion. The mouths, or the inhalent openings, 
are upon the outside of the pyrosoma, and the exhalent 
upon the inside. Each individual of the colony is con- 
tinually engaged in drawing in water, sifting out the_parti- 
cles of food, and ejecting it from the interior opening, all 
these little currents finding their way out of the single 
large opening, the combined volume forcing the entire 
colony along. 
Notr.—The pyrosoma is one of the most wonderful animals of the 
sea in its illuminating properties. In the southern seas they resemble 
bodies heated to a white heat, illuminating the greater depths, so that 
the forms of sharks, porpoises, and other larger animals are seen dis- 
tinctly far below ; and when at the surface light up the sails, masts, and 
