ASaiDIAE LUCIAE PYROSOMATIDAE 



91 



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 hy gemmation from a stolonic prolongation of an 

 imperfect 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 Pyeosomatidae, 

 containing one well-marked genus Pyrosoma, Peron, with about six 

 species. They are found swimming near the surface of the sea, 



Fig. 56. — Pyrosoma. A, lateral view (nat. size) ; B, end view ; C, diagram of longitudinal 

 section, at. Atrial apertures ; br, branchial apertures ; c.cl, common cloaca ; end, 

 endostyle ; t, test ; -o, velum or diaphragm at terminal opening. 



chiefly in tropical latitudes, and are brilliantly phosphorescent. 

 A fully developed Pyrosoina 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 Pig. 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 



