III ASCIDIAE LUCIAE—PYROSOMATIDAE OI 
atrial apertures on the inner surface next to the central cavity of 
the colony. They are placed with their ventral surfaces towards 
the closed end (Fig. 56, C). The first ascidiozooids of a colony 
are produced by gemmation from a stolonic prolongation of an 
unperfect oozooid or rudimentary larva (the “ cyathozooid ”), 
developed sexually. The subsequent ascidiozooids are formed 
from these as buds on a ventral stolon. 
This sub-order includes a single family, the PYROSOMATIDAE, 
containing one well-marked genus Pyrosoma, Péron, with about six 
species. They are found swimming near the surface of the sea, 
Fic. 56.—Pyrosoma. A, lateral view (nat. size) ; B, end view ; C, diagram of longitudinal 
section. aft, Atrial apertures ; br, branchial apertures ; c.c/, common cloaca ; end, 
endostyle ; ¢, test ; v, velum or diaphragm at terminal opening. 
chiefly in tropical latitudes, and are brilliantly phosphorescent. 
A fully developed Pyrosoma colony may be from an inch or two 
to upwards of twelve feet in length. 
The .Colony.—The shape of the colony is seen in Fig. 56, A. 
It tapers slightly towards the closed end, which is rounded. The 
opening at the opposite end may be reduced in size (see B and C), 
by the presence of a membranous prolongation of the common 
test, which can be contracted or expanded by means of the 
muscle-bands it receives from the atrial siphons of neighbouring 
zooids. The branchial apertures of the ascidiozooids are mostly 
placed upon short (in some cases longer) papillae projecting from 
the general surface, and many of the ascidiozooids have long conical 
processes of the test extending outwards beyond their branchial 
